ERC-721

ERC-721 is a standard interface for non-fungible tokens, where each token is unique and individually identified, unlike interchangeable ERC-20 tokens.

This standard underlies most well-known NFT collections, defining how ownership and transfer of each individual, unique token is tracked on-chain. The standard also defines a tokenURI function that points to a token's descriptive metadata (see Kaavon's "NFT Metadata" glossary definition) — royalty payments on resale are not part of ERC-721 itself, and are instead typically handled by a marketplace's own logic (see Kaavon's "NFT Royalty" glossary definition).