CoinJoin is a layer built on top of the Bitcoin blockchain with the aim of introducing more privacy to transactions.

The process requires finding different Bitcoin users who want to mix their sats and create a joint transaction. With this transaction, users send their respective Bitcoin to an address in identical amounts and then receive the same amount of Bitcoin they sent back (minus mining fees).

The transaction then returns Bitcoin to those users in identical amounts, which would make it impossible to differentiate each user based on CoinJoin transactions.