Fees paid to miners in order to validate a transaction on the Ethereum blockchain.

On the Ethereum blockchain, you need ETH to pay for gas fees. Gas is the unit of measure for how much computational work is required to process transactions and smart contracts on Ethereum.

Ethereum gas fees are often denominated in 'Gwei', which is a unit of measure for the Ether cryptocurrency (1 billion Gwei = 1 ETH).

More complex smart contracts, and code, will require more gas to execute, in the same way that a bigger, more powerful car takes more gas to run.

Under EIP-1559, the latest proposal for managing gas fees, users pay a base fee, which is the minimum amount of gas required to include a transaction in the next block, and a priority fee, which is basically a tip to miners. You can set the value of your priority fee based on how quickly you want your transaction to go through.

A gas limit is the maximum number of units of gas you are willing to pay in order to carry out a transaction on the Ethereum blockchain. A standard transaction sending ETH normally costs 21,000 gwei.