A term native to the Ethereum network which refers to the payment for transactions and contract services.
Gas refers to the payment or pricing structure on the Ethereum blockchain which underlines every transaction and contract execution. In other words, for every transaction, a user on the Ethereum network has to pay gas fees. The exact fees, however, are not determined by the network’s administrators, but by miners who the network compensates for their work in the verification of transactions. Even so, these miners cannot set arbitrary prices but have to look at demand and supply before deciding on gas fees.
Although gas was originally derived from the ether (ETH), there are price conversion mechanisms to get gas equivalents in other cryptos. Nevertheless, gas fees are still more traditionally used on the Ethereum network.