Gas is the term used to refer to the fee required to successfully execute a contract, or make a sale, on the Ethereum blockchain. Because Ethereum is a decentralized, open-source network, gas fees support the computer processing and the individuals (called “miners”) who keep the system working properly.
When there is more demand for ETH (the currency of the Ethereum blockchain) or when a large number of contracts need to be executed, gas prices will usually increase to ensure contracts are executed correctly and not ignored by miners.
A “gas limit” refers to the maximum price you’re willing to pay to execute a contract.