Non-fungible token

Non-fungible means each unit is unique and not interchangeable — your concert ticket has a specific seat and date, it's not equivalent to someone else's. On-chain, a non-fungible token tracks individual items by ID: the contract stores owner[tokenId] = address rather than a balance per account, so every token has a distinct identity and can carry its own metadata (URL, traits, provenance). NFT is the common name for the category. The Ethereum standard is ERC-721 — one ID, one owner, one contract. ERC-1155 generalises this to support both fungible and non-fungible tokens in the same contract, which is why it dominates in gaming (you want 100 identical potions and one unique sword in one inventory). The opposite concept is a fungible token — 1 USDC equals any other 1 USDC, no individuality.