What is NFT?
Also called: non-fungible token
An NFT is a token with a unique identifier, so each unit is distinguishable from every other. It is used for ownership records where individual identity matters, not interchangeable value.
In practice
The token records ownership; what it points to varies. Art and collectibles were the first use, but the durable applications are closer to credentials, tickets, in-game items, and domain names. Where the referenced media is stored, onchain or on a server someone pays for, determines whether it survives.