ERC-721 defines an interface for non-fungible tokens. Within a contract, a token identifier distinguishes one token from another, and an ownership query identifies the address that currently holds it. The meaningful identifier includes both the contract address and token ID on a particular network. Token number seven in one collection has no automatic relationship to number seven elsewhere. Applications use the common interface to display ownership, transfer tokens, and manage approvals without needing a different integration for every collection.

An optional metadata interface can connect a token to a name, description, or media reference. Suppose a token URI points to a JSON file on a project-controlled server. The on-chain ownership record can remain unchanged while that server changes the displayed image or stops responding. Safe-transfer functions also check whether a receiving contract supports the expected receiver interface, reducing one class of accidental delivery failure. That compatibility check does not verify the recipient's intentions or make a marketplace transaction economically fair.

Owning an ERC-721 token does not, by itself, convey copyright in an associated image, ownership of a physical object, or a guaranteed right to redeem a service. Those claims depend on additional terms and implementation. Approval settings likewise deserve attention because an authorized operator may have transfer power over more than one token. Research should distinguish the token's technical ownership, the availability and mutability of metadata, and the legal or contractual rights a project claims to attach. The standard directly establishes only its specified interface behavior.