Gas fees are transaction fees paid to validators for executing operations on a blockchain. The term comes from Ethereum. Every operation (sending a token, executing a smart contract, writing data) requires computational resources. Gas measures that resource consumption. Different operations cost different amounts of gas.
Sending a simple transaction costs less gas than executing a complex smart contract. You set a gas price to indicate how much you're willing to pay per unit of gas. The higher you set it, the sooner miners include your transaction. When the network is congested, gas prices spike. During periods of low activity, they're cheap. This creates feedback.
High fees incentivize users to wait or use cheaper blockchains. This might reduce demand and lower fees. Or they might just accept the high fees if the transaction is important. Gas fees are one of the biggest UX friction points in blockchain. A simple transaction might cost 20 dollars during congestion. A complex interaction might cost 100 dollars.
This makes blockchain unusable for small transactions. Layer 2 solutions batch transactions and post them to mainnet, reducing per-transaction costs. But today, if you're using Ethereum directly and the network is busy, expect to pay. Understanding gas is essential for blockchain development and usage.