Gas

Gas is the unit that measures how much computational work a transaction requires on Ethereum and similar smart-contract blockchains, and paying for it is how users compensate the network for executing their operations. Every action has a gas cost defined by the protocol: a simple ETH transfer costs a fixed 21,000 gas, while interacting with a complex smart contract — a token swap, an NFT mint — consumes far more because it triggers more computation and storage.

The total fee you pay is gas used multiplied by the price per unit of gas, which fluctuates with demand for block space. Since Ethereum's EIP-1559 upgrade in 2021, that price has two parts: a protocol-set base fee that is burned (destroyed), and an optional tip that goes to the block proposer to prioritize your transaction. For example, swapping tokens on a decentralized exchange might consume around 150,000 gas; when the network is quiet that can cost a fraction of a dollar, but during a popular NFT launch the same swap can cost many times more.

A common misconception is that gas is a separate token you must buy; gas is only a unit of measurement, and fees are paid in the chain's native coin — ETH on Ethereum. Gas serves a security purpose beyond payment: because every computational step costs something, it is economically impossible to spam the network with infinite loops or free denial-of-service attacks.