Gas is the unit of computational work on the Ethereum network; the word is also used for the fee paid to execute a transaction or smart contract. More broadly, it means a network fee.
In plain words
Every operation on Ethereum needs computation, and the fee paid for it is called gas. It equals the amount of gas the operation needs multiplied by the price of one unit of gas, usually quoted in gwei (one billionth of an ETH). A more complex operation and a busier network mean more expensive gas. The fee is charged even if the transaction fails. Other networks have their own mechanisms: on TRON the fee is expressed in Energy and Bandwidth resources.
Sources
- ethereum.org: Gas and fees — Gas and fees page. Checked 14.10.2026.
Example. You send USDT on the ERC-20 network: besides the amount, you need some ETH in the wallet because the gas is charged in it. Without ETH the transaction will not go through.