NFTs are not one thing — they are defined by token standards, and the standard determines what the token can do. The most common is ERC-721, where every token ID is unique and non-fungible. ERC-1155 is a multi-token standard: a single contract can hold fungible, semi-fungible, and non-fungible tokens, which is why game items and editions often use it. ERC-4907 adds a rental role, separating ownership from usage rights.

Standards matter because wallets, marketplaces, and DeFi protocols only support what they can read. A token that does not implement the expected interface may be invisible to marketplaces or impossible to list.

ERC-721: one contract, many unique token IDs, one owner per ID.
ERC-1155: batch transfers and mixed token types in one contract.
ERC-2981: on-chain royalty information, though enforcement is marketplace-dependent.

Standard	Fungibility	Typical use
ERC-721	Non-fungible	Art, collectibles, PFPs
ERC-1155	Mixed	Game items, editions
ERC-4907	Non-fungible + rental	Rental markets, gaming