In the Ethereum network, 'Gas' is a unit that measures the amount of computational work required to perform operations, including executing smart contracts and processing transactions. Every operation has a specified gas cost, which is paid in Ether, Ethereum's native cryptocurrency. Gas serves to prevent spam and ensure that network resources are allocated efficiently. The gas price is determined by the market and can fluctuate based on demand for network usage. Each transaction must include a gas limit (the maximum amount of gas the user is willing to use for the transaction) and a gas price (the price per gas unit in Ether).