Base Fee
The minimum fee per unit of gas that every transaction in an Ethereum block must pay, set by the protocol and destroyed.
The protocol computes the base fee from how full the previous block was, raising it when blocks run above the target size and lowering it when they run below, by a bounded step each block. Because the amount is fixed by the protocol rather than bid, a wallet can estimate the cost of the next block accurately instead of guessing in an auction. The base fee is burned rather than paid to the block producer, so heavy use of the network removes units from supply instead of increasing what validators receive. Readers meet it in wallet fee screens, where it is shown separately from the optional tip, and in dashboards that track how much has been burned.
In practice
When blocks run consistently above the target size, the base fee rises block after block until demand falls back toward the target.
The common misunderstanding
The base fee is not paid to miners or validators; it is destroyed, so congestion reduces supply rather than paying block producers more.