We can inform you that the term gas is taken from the similarity of the fee with the fuel that will keep the vehicle running. This gas fee is calculated in units of gas which is a quantitative measure for processing blockchain transactions.
The term "gas fee" is used by ethereum and polygon, while other blockchains such as solana and bitcoin use the term "transaction fee". Each transaction has a different amount of gas, depending on its complexity, the more complex the transaction or smart contract, the more gas is released.
The gas fee depends on the volume of demand and supply, so the gas fee is very volatile. When demand is high, the gas fee will increase while when demand is low, the gas fee will also decrease.