The standard for non-fungible tokens, where each token ID is unique and individually owned rather than interchangeable.
Where erc-20 tokens are interchangeable units, ERC-721 tokens are distinct items with their own IDs and metadata. That is the technical basis of an nft.
Each transfer moves one specific item, so marketplaces track per-item price history and a collection-level nft-floor-price rather than a single quote. Liquidity is correspondingly poor: there is no order book depth for a unique item.
Note that the metadata, and often the image itself, usually lives off-chain at a URL the contract points to. If that server or its funding disappears, the token remains but what it displays may not.
Original diagrams for the ideas on this page. Illustrative, not real market data.
The bid-ask spread. Buy orders sit below, sell orders above, and the gap between the best bid (50.01) and best ask (50.04) is the spread you pay to cross. Bar length shows the size resting at each price.
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