Mutual funds are a form of investment that pool money from various investors to purchase securities such as stocks, bonds, and other assets. When an investor sells their units of mutual fund, they are essentially selling their share of the fund's assets. This can be done through the fund manager or on a secondary market. Selling mutual fund units allows investors to liquidate their investment and potentially earn a profit or mitigate losses. It is important to understand the process and potential implications before making any decisions regarding the sale of mutual fund units.