Gas
The unit measuring computational work on Ethereum, paid as a fee to validators for executing transactions.
Gas quantifies how much computational effort a transaction or smart contract call requires on Ethereum. Simple ETH transfers cost 21,000 gas; complex DeFi interactions can cost millions. Users set a gas price (in gwei — billionths of ETH) they're willing to pay per unit of gas.
EIP-1559 (August 2021) introduced a base fee that adjusts dynamically with network demand and is burned (removed from supply), plus an optional priority tip to incentivise validators to include the transaction quickly.
Gas acts as both a spam deterrent and a mechanism to prioritise transactions. When the network is congested, gas prices spike; Layer 2 rollups process transactions off-chain in batches to dramatically reduce per-transaction gas costs.