A covered call strategy generally combines exposure to stocks or an index with selling call options. The option buyer pays a premium for the right to buy at a set price. A fund can use premiums to support distributions, but the payment is not guaranteed income or a measure of total return.
If the market rises above an option's strike price, the fund may give up some gains on the assets covered by the calls. If the market falls, the premium may provide a cushion, but it cannot prevent losses in the underlying portfolio. The amount of upside traded away depends on how many calls the fund writes and how it sets the strike prices and expirations.
Questions to ask: What does the fund own? How much of the portfolio is covered by calls? How have NAV and market-price total returns behaved in rising and falling markets? What does the latest distribution notice say about payment sources?
Further reading: Investor.gov: Mutual Funds and ETFs