ERC-721 stands for Ethereum Request for Comment 721. It is a widely adopted Ethereum token standard that defines a set of rules and guidelines for the creation and implementation of non-fungible tokens (NFTs) on the Ethereum blockchain. The ERC-721 standard was proposed by William Entriken, Dieter Shirley, Jacob Evans, Nastassia Sachs, and Robby Dermody in 2017.

Unlike fungible tokens such as cryptocurrencies (e.g., ERC-20 tokens), which are interchangeable and have the same value, ERC-721 tokens are unique and indivisible. Each ERC-721 token represents a distinct digital asset, such as collectibles, artwork, virtual real estate, or in-game items. The standard specifies how NFT ownership is tracked and transferred between Ethereum addresses.

ERC-721 has played a pivotal role in the explosion of the NFT market, enabling the creation of digital assets with verifiable scarcity, provenance, and ownership. It has paved the way for various innovative applications and use cases across industries, including art, gaming, decentralized finance, and more. The standard has also inspired the development of subsequent token standards, such as ERC-1155, which combines fungible and non-fungible features.