Overview
Gas price is typically measured in 'Gwei' (a tiny fraction of Ether). It represents the 'bid' a user makes to have their transaction included in the next block.
Market Dynamics
Validators prioritize transactions with higher gas prices because they earn more from them. During times of high demand, gas prices can spike significantly, making transactions expensive.
EIP-1559
Ethereum's 2021 upgrade introduced a 'base fee' that is burned and a 'priority fee' (tip) that goes to validators, making gas prices more predictable.