A service that mixes a cryptocurrency transaction with other transactions to eliminate the possibility of someone discovering the party that originated them. The cryptocurrency blockchain is a public record, and with the proper analysis tools, a sender's wallet can be uncovered and ultimately reveal the owner's name. If a sender is afraid of being identified when sending Bitcoins or some other crypto token, a tumbler service can be used.
Also called "cryptocurrency mixing," the tumbler service functions like a VPN, which hides the sending address from the receiving party. The coins are sent to the tumbler service, and the service relays the transaction hiding the sender's address. The amount of coins may also be split up to further randomize the transaction, and the tumbler takes a fee like a foreign currency exchange. See cryptocurrency