Fully diluted valuation, or FDV, estimates what a cryptocurrency would be worth if every coin that will ever exist were already in circulation. It is calculated by multiplying the current price by the maximum supply, rather than the circulating supply used for market cap.
FDV is useful because it highlights future issuance. If a project has many coins still to be released, its FDV can be far higher than its current market cap. That gap signals that more supply is coming, which is worth being aware of when reading a project figures.
Like any single metric, FDV should be read with context. A large gap between market cap and FDV is not automatically good or bad; it simply reflects how much supply has yet to enter circulation. It is one lens among several for understanding a project scale.