Putnam Municipal
Opportunities
Trust

Annual report
4 | 30 | 18

Consider these risks before investing: Lower-rated bonds may offer higher yields in return for more risk. Bond investments are subject to interest-rate risk (the risk of bond prices falling if interest rates rise) and credit risk (the risk of an issuer defaulting on interest or principal payments). Interest-rate risk is greater for longer-term bonds, and credit risk is greater for below-investment-grade bonds. Unlike bonds, funds that invest in bonds have fees and expenses. Bond prices may fall or fail to rise over time for several reasons, including general financial market conditions, changing market perceptions (including perceptions about the risk of default, and expectations about monetary policy or interest rates), changes in government intervention in the financial markets, and factors related to a specific issuer or industry. These and other factors may lead to increased volatility and reduced liquidity in the fund’s portfolio holdings. You can lose money by investing in the fund. The fund’s shares trade on a stock exchange at market prices, which may be lower than the fund’s net asset value.

Message from the Trustees

June 14, 2018

Dear Fellow Shareholder:

After an extended period of record advances and low volatility for global financial markets, the first half of 2018 has been considerably more challenging. Stocks began the year against a backdrop of optimism, but quickly lost ground in February with a sharp downturn that pushed the U.S. market into correction territory. Stocks subsequently recovered somewhat, but markets have remained choppy. Bond markets have also had a series of ups and downs, due in part to uncertainty surrounding trade policy and the trajectory of U.S. interest rates.

While volatility and declines can be unsettling, seasoned investors recognize that they are natural and ultimately can restore balance in the financial markets. In this changing environment, Putnam’s experienced investment professionals continue to monitor risks and seek opportunities. They take a research-intensive approach to investing that includes risk management strategies designed to serve investors in all types of markets.

As always, we believe investors should maintain a well-diversified portfolio, think about long-term goals, and speak regularly with their financial advisors. In the following pages, you will find an overview of your fund’s performance for the reporting period as well as an outlook for the coming months.

Thank you for investing with Putnam.

Putnam Municipal Opportunities Trust has the flexibility to invest in municipal bonds issued by any state in the country or U.S. territory. As a closed-end fund, it shares some common characteristics with open-end mutual funds, but there are some key differences that investors should understand as they consider their portfolio.

Looking at a closed-end fund’s performance

You will usually see that the NAV and the market price differ. The market price can be influenced by several factors that cause it to vary from the NAV, including fund distributions, changes in supply and demand for the fund’s shares, changing market conditions, and investor perceptions of the fund or its investment manager.

A mix of credit qualities

In addition to its flexible geographical focus, Putnam Municipal Opportunities Trust combines bonds of differing credit quality. The fund invests in high-quality bonds, but also includes an allocation to lower-rated bonds, which may offer higher income in return for more risk.

Data are historical. Past performance does not guarantee future results. More recent returns may be less or more than those shown. Investment return and net asset value will fluctuate, and you may have a gain or a loss when you sell your shares. Performance assumes reinvestment of distributions and does not account for taxes. Fund returns in the bar chart are at NAV. See below and pages 9–10 for additional performance information, including fund returns at market price. Index and Lipper results should be compared with fund performance at NAV. Fund results reflect the use of leverage, while index results are unleveraged and Lipper results reflect varying use of, and methods for, leverage.

This comparison shows your fund’s performance in the context of broad market indexes for the 12 months ended 4/30/18. See above and pages 9–10 for additional fund performance information. Index descriptions can be found on page 11.

Paul holds a B.A. from Suffolk University. He has been in the investment industry since he joined Putnam in 1989.

In addition to Paul, your fund is managed by Garrett L. Hamilton, CFA.

Paul, how was the market for municipal bonds during the reporting period?

After rallying in the early months of the period, volatility picked up in the municipal bond market during the second half of the period in response to higher interest rates and the passage of the Tax Cuts and Jobs Act. With the new tax law eliminating advanced refundings, bond issuers rushed to issue new deals before the legislation took effect in 2018, resulting in heavier near-term municipal bond supply. Total municipal bond new-issue volume for December 2017 was $62.5 billion — surpassing the previous record of $52.7 billion in December 1985, which was just before the last comprehensive tax overhaul took effect. However, the flood of new issuance was well received by investors, and the municipal bond market rallied as strong demand helped buoy prices.

The Federal Reserve announced three interest-rate hikes during the period, raising the federal funds rate in June and December of 2017 and in March 2018. At period end, the federal funds rate stood at a target range of 1.50% to 1.75%. With interest rates rising, municipal bonds outperformed U.S. Treasuries and the broader

Credit qualities are shown as a percentage of the fund’s net assets (common and preferred shares) as of 4/30/18. A bond rated BBB or higher (SP-3 or higher, for short-term debt) is considered investment grade. This chart reflects the highest security rating provided by one or more of Standard & Poor’s, Moody’s, and Fitch. Ratings may vary over time.

Cash and net other assets, if any, represent the market value weights of cash, derivatives, and short-term securities in the portfolio. The fund itself has not been rated by an independent rating agency.

Top ten state allocations are shown as a percentage of the fund’s net assets (common and preferred shares) as of 4/30/18. Summary information may differ from the portfolio schedule included in the financial statements due to the differing treatment of interest accruals, the floating-rate portion of tender-option bonds, derivative securities, if any, the use of different classifications of securities for presentation purposes, and rounding. Holdings and allocations may vary over time.

fixed-income markets during the period. [Bond prices generally fall as rates rise.]

How did the fund perform during the reporting period?

For the 12 months ended April 30, 2018, the fund outperformed its benchmark, the Bloomberg Barclays Municipal Bond Index, and the average return of its Lipper peer group, General & Insured Municipal Debt Funds (leveraged closed-end).

What was your investment strategy in this environment?

Given our outlook for interest rates trending higher, the fund began the period with more of a barbell approach to structuring the portfolio — overweighting short-term bonds, underweighting intermediate-term bonds with maturities of 5 to 10 years, and overweighting bonds with maturities of 11 to 16 years. However, with the flattening of the yield curve that materialized as the period progressed, we began steering the portfolio away from the short and long ends of the curve and focusing more on bonds with maturities of 15 to 20 years where we saw better value.

Duration positioning, which affects the portfolio’s sensitivity to interest rates, was generally neutral relative to the benchmark index. From a credit-quality standpoint, the fund held an overweight exposure to higher-quality bonds rated A and BBB. From a sector-positioning perspective, we placed greater focus on higher education, essential service utilities, and continuing-care retirement community bonds relative to the fund’s Lipper group. This strategy was positive for performance results.

We maintained an underweight position in Puerto Rico-based issuers relative to the fund’s Lipper peers. Puerto Rico’s current economic and financial situation remains extremely difficult and could further challenge the debt restructuring process, in our view. This underweight exposure aided performance, as Puerto Rico debt generally declined during the period. By the close of the period, the fund no longer held investments in Puerto Rico.

The fund reduced its dividend rate during the reporting period. What led to that decision?

Since the fund is leveraged through the use of preferred shares, costs to the portfolio have risen, as prevailing short-term interest rates have climbed more than long-term rates, which are still relatively low, historically speaking. Accordingly, the fund’s monthly dividend rate declined from $0.0541 to $0.0461 in February 2018.

What are your thoughts about the new tax law and its effects on the municipal bond market?

The Tax Cuts and Jobs Act reduced corporate tax rates and to a lesser extent, individual rates; changed some popular deductions; and eliminated advance refundings for municipal issuers. However, the tax-exempt status of municipal bonds remains intact. As such, we do not believe the new tax law will materially affect demand for municipal bonds from individuals. However, in our view, the reduction in corporate taxes may lower demand from banks, property and casualty insurers, or other corporate buyers.

The legislation, in our view, will have a more meaningful positive impact on the supply side of the technical equation. We believe the elimination of advance refundings could remove up to 20% of the municipal market’s annual supply — a fairly significant portion of the municipal bond supply.

What is your outlook for interest rates in the coming months?

Jerome Powell was sworn in as the new Federal Reserve chair on February 5, 2018. Investors generally believe that Chairman Powell will implement the plan laid out by his predecessor, Janet Yellen, for gradual rate increases. At the Fed’s first meeting under Chairman Powell in March 2018, the central bank reiterated its plan for three interest-rate hikes this year but hinted that it would be open to the possibility of a fourth hike if necessary to keep the U.S. economy from overheating. The Fed also revised its outlook for three rate hikes in 2019 instead of two, and projected the unemployment rate, which stood at 4.1% at period-end, would fall to 3.8% in 2018.

We expect that solid global economic growth will facilitate the continued normalization of short-term interest rates from their still historic lows and the continued flattening of the yield curve, with short-term rates rising more than long-term rates. Should incoming data signal a strengthening economic outlook, we believe the Fed might be inclined to tighten a little faster to keep inflationary pressures at bay or, conversely, tighten more slowly if fiscal policy proves less stimulative.

Broadly speaking, the municipal bond market continues to adjust to fluctuating supply and demand conditions created by the new tax legislation. In our view, the asset class offers a high-quality, low-default investment option for investors seeking attractive tax-free income and diversification opportunities.

Thank you, Paul, for your time and insights today.

The views expressed in this report are exclusively those of Putnam Management and are subject to change. They are not meant as investment advice.

Please note that the holdings discussed in this report may not have been held by the fund for the entire period. Portfolio composition is subject to review in accordance with the fund’s investment strategy and may vary in the future. Current and future portfolio holdings are subject to risk. Statements in the Q&A concerning the fund’s performance or portfolio composition relative to those of the fund’s Lipper peer group may reference information produced by Lipper Inc. or through a third party.

This chart shows how the fund’s top weightings have changed over the past six months. Allocations are shown as a percentage of the fund’s net assets (common and preferred shares). Current period summary information may differ from the information in the portfolio schedule notes included in the financial statements due to the inclusion of derivative securities, any interest accruals, the use of different classifications of securities for presentation purposes, and rounding. Holdings and allocations may vary over time.

Your fund’s performance

This section shows your fund’s performance, price, and distribution information for periods ended April 30, 2018, the end of its most recent fiscal year. In accordance with regulatory requirements for mutual funds, we also include performance information as of the most recent calendar quarter-end. Performance should always be considered in light of a fund’s investment strategy. Data represent past performance. Past performance does not guarantee future results. More recent returns may be less or more than those shown. Investment return, net asset value, and market price will fluctuate, and you may have a gain or a loss when you sell your shares.

Fund performance Total return and comparative index results for periods ended 4/30/18

Performance assumes reinvestment of distributions and does not account for taxes.

Index and Lipper results should be compared with fund performance at net asset value. Fund results reflect the use of leverage, while index results are unleveraged and Lipper results reflect varying use of, and methods for, leverage.

^* Over the 1-year, 3-year, 5-year, 10-year, and life-of-fund periods ended 4/30/18, there were 61, 61, 61, 53, and 26 funds, respectively, in this Lipper category.

Performance includes the deduction of management fees and administrative expenses.

Fund price and distribution information For the 12-month period ended 4/30/18

The classification of distributions, if any, is an estimate. Final distribution information will appear on your year-end tax forms.

¹ For some investors, investment income may be subject to the federal alternative minimum tax. Income from federally exempt funds may be subject to state and local taxes.

² Capital gains, if any, are taxable for federal and, in most cases, state purposes.

³ Most recent distribution, including any return of capital and excluding capital gains, annualized and divided by NAV or market price at end of period.

⁴ Assumes maximum 40.80% federal tax rate for 2018. Results for investors subject to lower tax rates would not be as advantageous.

Fund performance as of most recent calendar quarter Total return for periods ended 3/31/18

See the discussion following the fund performance table on page 9 for information about the calculation of fund performance.

Terms and definitions

Important terms

Total return shows how the value of the fund’s shares changed over time, assuming you held the shares through the entire period and reinvested all distributions in the fund.

Net asset value (NAV) is the value of all your fund’s assets, minus any liabilities, divided by the number of outstanding shares.

Market price is the current trading price of one share of the fund. Market prices are set by transactions between buyers and sellers on exchanges such as the New York Stock Exchange.

Fixed-income terms

Current rate is the annual rate of return earned from dividends or interest of an investment. Current rate is expressed as a percentage of the price of a security, fund share, or principal investment.

Yield curve is a graph that plots the yields of bonds with equal credit quality against their differing maturity dates, ranging from shortest to longest. It is used as a benchmark for other debt, such as mortgage or bank lending rates.

Comparative indexes

Bloomberg Barclays Municipal Bond Index is an unmanaged index of long-term fixed-rate investment-grade tax-exempt bonds.

Bloomberg Barclays U.S. Aggregate Bond Index is an unmanaged index of U.S. investment-grade fixed-income securities.

ICE BofAML (Intercontinental Exchange Bank of America Merrill Lynch) U.S. 3-Month Treasury Bill Index is an unmanaged index that seeks to measure the performance of U.S. Treasury bills available in the marketplace.

S&P 500 Index is an unmanaged index of common stock performance.

ICE Data Indices, LLC (“ICE BofAML”), used with permission. ICE BofAML permits use of the ICE BofAML indices and related data on an “as is” basis; makes no warranties regarding same; does not guarantee the suitability, quality, accuracy, timeliness, and/or completeness of the ICE BofAML indices or any data included in, related to, or derived therefrom; assumes no liability in connection with the use of the foregoing; and does not sponsor, endorse, or recommend Putnam Investments, or any of its products or services.

Indexes assume reinvestment of all distributions and do not account for fees. Securities and performance of a fund and an index will differ. You cannot invest directly in an index.

Lipper is a third-party industry-ranking entity that ranks mutual funds. Its rankings do not reflect sales charges. Lipper rankings are based on total return at net asset value relative to other funds that have similar current investment styles or objectives as determined by Lipper. Lipper may change a fund’s category assignment at its discretion. Lipper category averages reflect performance trends for funds within a category.

Other information for shareholders

Important notice regarding share repurchase program

In September 2017, the Trustees of your fund approved the renewal of a share repurchase program that had been in effect since 2005. This renewal allows your fund to repurchase, in the 12 months beginning October 10, 2017, up to 10% of the fund’s common shares outstanding as of October 9, 2017.

Important notice regarding delivery of shareholder documents

In accordance with Securities and Exchange Commission (SEC) regulations, Putnam sends a single copy of annual and semiannual shareholder reports, prospectuses, and proxy statements to Putnam shareholders who share the same address, unless a shareholder requests otherwise. If you prefer to receive your own copy of these documents, please call Putnam at 1-800-225-1581, and Putnam will begin sending individual copies within 30 days.

Proxy voting

Putnam is committed to managing our mutual funds in the best interests of our shareholders. The Putnam funds’ proxy voting guidelines and procedures, as well as information regarding how your fund voted proxies relating to portfolio securities during the 12-month period ended June 30, 2017, are available in the Individual Investors section of putnam.com, and on the SEC’s website, www.sec.gov. If you have questions about finding forms on the SEC’s website, you may call the SEC at 1-800-SEC-0330. You may also obtain the Putnam funds’ proxy voting guidelines and procedures at no charge by calling Putnam’s Shareholder Services at 1-800-225-1581.

Fund portfolio holdings

The fund will file a complete schedule of its portfolio holdings with the SEC for the first and third quarters of each fiscal year on Form N-Q. Shareholders may obtain the fund’s Form N-Q on the SEC’s website at www.sec.gov. In addition, the fund’s Form N-Q may be reviewed and copied at the SEC’s Public Reference Room in Washington, D.C. You may call the SEC at 1-800-SEC-0330 for information about the SEC’s website or the operation of the Public Reference Room.

Trustee and employee fund ownership

Putnam employees and members of the Board of Trustees place their faith, confidence, and, most importantly, investment dollars in Putnam mutual funds. As of April 30, 2018, Putnam employees had approximately $510,000,000 and the Trustees had approximately $80,000,000 invested in Putnam mutual funds. These amounts include investments by the Trustees’ and employees’ immediate family members as well as investments through retirement and deferred compensation plans.

Important notice regarding Putnam’s privacy policy

In order to conduct business with our shareholders, we must obtain certain personal information such as account holders’ names, addresses, Social Security numbers, and dates of birth. Using this information, we are able to maintain accurate records of accounts and transactions.

It is our policy to protect the confidentiality of our shareholder information, whether or not a shareholder currently owns shares of our funds. In particular, it is our policy not to sell information about you or your accounts to outside marketing firms. We have safeguards in place designed to prevent unauthorized access to our computer systems and procedures to protect personal information from unauthorized use.

Under certain circumstances, we must share account information with outside vendors who provide services to us, such as mailings and proxy solicitations. In these cases, the service providers enter into confidentiality agreements with us, and we provide only the information necessary to process transactions and perform other services related to your account. Finally, it is our policy to share account information with your financial representative, if you’ve listed one on your Putnam account.

Summary of Putnam Closed-End Funds’ Amended and Restated Dividend Reinvestment Plans

Putnam High Income Securities Fund, Putnam Managed Municipal Income Trust, Putnam Master Intermediate Income Trust, Putnam Municipal Opportunities Trust and Putnam Premier Income Trust (each, a “Fund” and collectively, the “Funds”) each offer a dividend reinvestment plan (each, a “Plan” and collectively, the “Plans”). If you participate in a Plan, all income dividends and capital gain distributions are automatically reinvested in Fund shares by the Fund’s agent, Putnam Investor Services, Inc. (the “Agent”). If you are not participating in a Plan, every month you will receive all dividends and other distributions in cash, paid by check and mailed directly to you.

Upon a purchase (or, where applicable, upon registration of transfer on the shareholder records of a Fund) of shares of a Fund by a registered shareholder, each such shareholder will be deemed to have elected to participate in that Fund’s Plan. Each such shareholder will have all distributions by a Fund automatically reinvested in additional shares, unless such shareholder elects to terminate participation in a Plan by instructing the Agent to pay future distributions in cash. Shareholders who were not participants in a Plan as of January 31, 2010, will continue to receive distributions in cash but may enroll in a Plan at any time by contacting the Agent.

If you participate in a Fund’s Plan, the Agent will automatically reinvest subsequent distributions, and the Agent will send you a confirmation in the mail telling you how many additional shares were issued to your account.

To change your enrollment status or to request additional information about the Plans, you may contact the Agent either in writing, at P.O. Box 8383, Boston, MA 02266-8383, or by telephone at 1-800-225-1581 during normal East Coast business hours.

How you acquire additional shares through a Plan If the market price per share for your Fund’s shares (plus estimated brokerage commissions) is greater than or equal to their net asset value per share on the payment date for a distribution, you will be issued shares of the Fund at a value equal to the higher of the net asset value per share on that date or 95% of the market price per share on that date.

If the market price per share for your Fund’s shares (plus estimated brokerage commissions) is less than their net asset value per share on the payment date for a distribution, the Agent will buy Fund shares for participating accounts in the open market. The Agent will aggregate open-market purchases on behalf of all participants, and the average price (including brokerage commissions) of all shares purchased by the Agent will be the price per share allocable to each participant. The Agent will generally complete these open-market purchases within five business days following the payment date. If, before the Agent has completed open-market purchases, the market price per share (plus estimated brokerage commissions) rises to exceed the net asset value per share on the payment date, then the purchase price may exceed the net asset value per share, potentially resulting in the acquisition of fewer shares than if the distribution had been paid in newly issued shares.

How to withdraw from a Plan Participants may withdraw from a Fund’s Plan at any time by notifying the Agent, either in writing or by telephone. Such withdrawal will be effective immediately if notice is received by the Agent with sufficient time prior to any distribution record date; otherwise, such withdrawal will be effective with respect to any subsequent distribution following notice of withdrawal. There is no penalty for withdrawing from or not participating in a Plan.

Plan administration The Agent will credit all shares acquired for a participant under a Plan to the account in which the participant’s common shares are held. Each participant will

be sent reasonably promptly a confirmation by the Agent of each acquisition made for his or her account.

About brokerage fees Each participant pays a proportionate share of any brokerage commissions incurred if the Agent purchases additional shares on the open market, in accordance with the Plans. There are no brokerage charges applied to shares issued directly by the Funds under the Plans.

About taxes and Plan amendments Reinvesting dividend and capital gain distributions in shares of the Funds does not relieve you of tax obligations, which are the same as if you had received cash distributions. The Agent supplies tax information to you and to the IRS annually. Each Fund reserves the right to amend or terminate its Plan upon 30 days’ written notice. However, the Agent may assign its rights, and delegate its duties, to a successor agent with the prior consent of a Fund and without prior notice to Plan participants.

If your shares are held in a broker or nominee name If your shares are held in the name of a broker or nominee offering a dividend reinvestment service, consult your broker or nominee to ensure that an appropriate election is made on your behalf. If the broker or nominee holding your shares does not provide a reinvestment service, you may need to register your shares in your own name in order to participate in a Plan.

In the case of record shareholders such as banks, brokers or nominees that hold shares for others who are the beneficial owners of such shares, the Agent will administer the Plan on the basis of the number of shares certified by the record shareholder as representing the total amount registered in such shareholder’s name and held for the account of beneficial owners who are to participate in the Plan.

Financial statements

These sections of the report, as well as the accompanying Notes, preceded by the Report of Independent Registered Public Accounting Firm, constitute the fund’s financial statements.

The fund’s portfolio lists all the fund’s investments and their values as of the last day of the reporting period. Holdings are organized by asset type and industry sector, country, or state to show areas of concentration and diversification.

Statement of assets and liabilities shows how the fund’s net assets and share price are determined. All investment and non-investment assets are added together. Any unpaid expenses and other liabilities are subtracted from this total. The result is divided by the number of shares to determine the net asset value per share. (For funds with preferred shares, the amount subtracted from total assets includes the liquidation preference of preferred shares.)

Statement of operations shows the fund’s net investment gain or loss. This is done by first adding up all the fund’s earnings — from dividends and interest income — and subtracting its operating expenses to determine net investment income (or loss). Then, any net gain or loss the fund realized on the sales of its holdings — as well as any unrealized gains or losses over the period — is added to or subtracted from the net investment result to determine the fund’s net gain or loss for the fiscal year.

Statement of changes in net assets shows how the fund’s net assets were affected by the fund’s net investment gain or loss, by distributions to shareholders, and by changes in the number of the fund’s shares. It lists distributions and their sources (net investment income or realized capital gains) over the current reporting period and the most recent fiscal year-end. The distributions listed here may not match the sources listed in the Statement of operations because the distributions are determined on a tax basis and may be paid in a different period from the one in which they were earned.

Financial highlights provide an overview of the fund’s investment results, per-share distributions, expense ratios, net investment income ratios, and portfolio turnover in one summary table, reflecting the five most recent reporting periods. In a semiannual report, the highlights table also includes the current reporting period.

Report of Independent Registered Public Accounting Firm

To the Trustees and Shareholders of
Putnam Municipal Opportunities Trust

Opinion on the Financial Statements

We have audited the accompanying statement of assets and liabilities, including the fund’s portfolio, of Putnam Municipal Opportunities Trust (the “Fund”) as of April 30, 2018, the related statements of operations and cash flows for the year ended April 30, 2018, the statement of changes in net assets for each of the two years in the period ended April 30, 2018, including the related notes, and the financial highlights for each of the five years in the period ended April 30, 2018 (collectively referred to as the “financial statements”). In our opinion, the financial statements present fairly, in all material respects, the financial position of the Fund as of April 30, 2018, the results of its operations and its cash flows for the year then ended, the changes in its net assets for each of the two years in the period ended April 30, 2018 and the financial highlights for each of the five years in the period ended April 30, 2018 in conformity with accounting principles generally accepted in the United States of America.

Basis for Opinion

These financial statements are the responsibility of the Fund’s management. Our responsibility is to express an opinion on the Fund’s financial statements based on our audits. We are a public accounting firm registered with the Public Company Accounting Oversight Board (United States) (“PCAOB”) and are required to be independent with respect to the Fund in accordance with the U.S. federal securities laws and the applicable rules and regulations of the Securities and Exchange Commission and the PCAOB.

We conducted our audits of these financial statements in accordance with the standards of the PCAOB. Those standards require that we plan and perform the audit to obtain reasonable assurance about whether the financial statements are free of material misstatement, whether due to error or fraud.

Our audits included performing procedures to assess the risks of material misstatement of the financial statements, whether due to error or fraud, and performing procedures that respond to those risks. Such procedures included examining, on a test basis, evidence regarding the amounts and disclosures in the financial statements. Our audits also included evaluating the accounting principles used and significant estimates made by management, as well as evaluating the overall presentation of the financial statements. Our procedures included confirmation of securities owned as of April 30, 2018 by correspondence with the custodian, and brokers; when replies were not received from brokers, we performed other auditing procedures. We believe that our audits provide a reasonable basis for our opinion.

PricewaterhouseCoopers LLP
Boston, Massachusetts
June 14, 2018

We have served as the auditor of one or more investment companies in the Putnam Investments family of mutual funds since at least 1957. We have not determined the specific year we began serving as auditor.

The fund’s portfolio 4/30/18

Key to holding’s abbreviations