Gas

Gas is the unit that measures how much computational work a transaction or smart-contract operation consumes on networks like Ethereum. Each operation costs a set amount of gas, so a simple transfer uses little while a complex contract uses more. Users set a gas limit to cap how much work they will pay for, guarding against runaway execution.

A common misconception is that gas is a separate coin; it is a measure of work, paid for in the networks own currency. See what gas fees pay for.