Blockchain bridges receive one type of crypto, for instance, LUNA. It locks this LUNA as a deposit. It 'mints' an equal amount of another cryptocurrency, like, Wrapped LUNA and releases it on another blockchain e.g. Ethereum Mainnet. There are two kinds of blockchain bridges, trusted bridges and trustless bridges.

source https://gadgets360.com/cryptocurrency/opinion/what-are-blockchain-bridges-2951725#rss-gadgets-all