A Bitcoin mixer (also known as a tumbler) is a service that provides a way to obscure the original source of a Bitcoin transaction. This is done by mixing different transactions together to make the transaction difficult to track.
The mixer takes a user’s coins, breaks them up into pieces, mixes them with coins from other users, and then sends them back to the user in a different form. This makes it difficult to determine the original sender and recipient of the coins.
The service is often used by people who wish to remain anonymous when making transactions with Bitcoin.