Glossary
ERC-721
Ethereum's standard interface for non-fungible tokens: each token has a unique ID, single owner, and (usually) a pointer to off-chain metadata.
ERC-721 fixes the function and event signatures every NFT contract
implements: ownerOf, transferFrom, approve, plus the
Transfer and Approval events. Each token has a uint256
ID; mints, transfers, and burns just update that ID's owner.
Metadata — image, name, attributes — is typically hosted off-chain
on IPFS, Arweave, or a regular web server, and pointed to via the
tokenURI function. Every NFT marketplace, wallet, and explorer
knows this interface, which is what made NFTs interoperable from
day one.