A blockchain name service is the phonebook of blockchain technology, just like the domain name service is for the classic internet. It is a decentralized human-readable address that is mapped to machine-readable identifiers and other resource. It usually takes the form “[username].[blockchain ticker]” for example, ced.eth, ced.sol, ced.ccd, for a user named ced on Ethereum, Solana and Concordium blockchains respectively. Other suffixes exists which do not necessarily relate to the chain on which the name lives, for example, .crypto, .nft, .x, .bitcoin, etcetera. While some are minted as an NFT, transferred to minters' wallet and owned lifelong, some are designed to be owned for a designated period specified at purchase before renewal is demanded.
Nowadays, these names commonly found on crypto Twitter, used as display names by crypto enthusiasts who may or may not have minted the blockchain names. These names make the blockchain technology user-friendly as it encapsulates the machine-level identifiers.