Gas refers to the fee, or pricing value, required to successfully conduct a transaction or execute a contract on the Ethereum blockchain platform. A transaction fee is determined by Gas Limit and Gas Price, which can be demonstrated as follows: Transaction fee = Gas Limit * Gas Price. Actually, the real amount of transaction fee is lower than this as the Gas Limit is the maximum value. However, if the Gas Limit is set too low, the transaction will be rejected but the Gas won’t be refunded. So users normally set a relatively high Gas Limit.