ERC-721 or Non-Fungible Token (NFT) is used to identify something
or someone in a unique way. It refers to a token standard that can
be found on the Ethereum blockchain.
NFTs are tokens that have unique characteristics, setting them
apart from other tokens.
References:
https://ethereum.org/en/developers/docs/standards/tokens/erc-721/
https://coinmarketcap.com/alexandria/glossary/erc-721