A Bitcoin transaction fee is a fee that is charged to users when they send a transaction over the Bitcoin network. This fee is paid to the miners who process transactions on the network, and is typically a small amount of Bitcoin (BTC) that is taken out of the total amount sent. The fee is usually calculated based on the size of the transaction and the current rate of mining fees. The higher the transaction fee, the more likely the transaction is to be included in the next block, and therefore, the faster it will be processed.