What are gas fees and why do they fluctuate so much?

Gas fees are the cost of doing anything on the Ethereum network - sending ETH, interacting with a DeFi protocol, minting an NFT, or swapping tokens. They are priced in Gwei (one billion Gwei equals one ETH) and change dynamically based on how much activity is competing for block space at any given moment. Think of it like surge pricing on a ride-share app: when network demand is high, fees spike. When demand is low, fees are minimal. The 2021 NFT boom sent gas fees to levels where a simple token transfer sometimes cost more than the token itself was worth. This painful experience accelerated the development of Layer 2 networks designed to process transactions at a fraction of the cost.