A fund of funds is a mutual fund that invests in other mutual funds or ETFs instead of buying shares and bonds itself.
A fund of funds, or FoF, puts its money into one or more other schemes. Common kinds in India:
An ETF FoF is not itself an ETF. It is bought and sold with the fund house at its NAV and accepts SIPs.
Costs come in two layers. You pay the FoF's own expense ratio and, indirectly, the expenses of the funds it holds. SEBI caps the combined total.
Tax depends on what the FoF holds, so it can differ from the tax on the fund it invests in. Mutual fund tax explains the rules by fund type.
International FoFs are also subject to an industry-wide ceiling on overseas investment by Indian mutual funds, and some have paused new purchases when it was reached.
Each fund page has its returns, risk, costs, managers and everything it holds.