what is the unit of fee for transactions on ethereum

The unit of fee for transactions on Ethereum is called "gas," which measures the amount of computational effort required for operations on the network. Gas fees are paid in a denomination of Ether called "gwei," where 1 gwei equals 10−910^{-9}10−9 ETH. For example, a simple transaction like sending ETH consumes 21,000 units of gas, and the fee is calculated as gas units multiplied by the gas price in gwei (tip plus base fee).