Gas is the processing fee for every transaction made in the Ethereum network.
To execute a smart contract on Ethereum’s blockchain, nodes must be paid according to the complexity of the smart contract.
This prevents accidental or malicious infinite loops coded within smart contracts which would result in overwhelming the computational resources of the Ethereum network.
Gas acts as a metering unit for executions performed on the EVM.
Gas units are a fixed number, depending on the computation, and paid with ether in a denomination called GWei.
Gas prices vary depending on how busy the Ethereum network is at any given time.