Bitcoin transaction fees give Bitcoin miners an incentive to include transactions into their blocks and provide sufficient hashing power, securing the Bitcoin network. Some also call it “miner fees”.
When making a transaction over the Bitcoin network, one usually pays for miners to facilitate the transaction. The fee tends to be around 0.0001-0.0015 Bitcoin. Block sizes are limited and can only support limited number of transactions. Therefore, miners will prioritize transactions that pay higher fees. A higher fee means the transaction can be processed sooner.
This raises the threshold of making Bitcoin transactions and also effectively protects the blockchain from spams while ensuring miners still have the incentive to maintain the Bitcoin network even after all the Bitcoins are mined.