Definition
Transaction fees are the difference between the total inputs and total outputs of a Bitcoin transaction. They serve as an incentive for miners to include transactions in their blocks and as a spam prevention mechanism. Fees are measured in satoshis per virtual byte (sat/vB).
As the block subsidy decreases over time through halvings, transaction fees become an increasingly important component of miner revenue. Fee levels fluctuate based on network demand and mempool congestion.
In Simple Terms
Fees users pay for miners to process their transactions. Becomes more important as block rewards decrease.
Fees paid by Bitcoin users to incentivize miners to include their transactions in a block. Higher fees mean faster confirmation.