Gwei is the denomination used to determine the gas price for any Ethereum transaction. It is one of the smallest units of ETH, often given by 10-9 ETH, or 0.00000001 ETH. Inversely, 1 ETH equals 1 Billion gwei. Gwei offers a convenient way to calculate the gas fee (gas price paid to the miners).
Over time, gwei has also acquired the nickname ‘Shannon,’ derived from Claude Shannon, the cryptographer, and mathematician known as ‘the father of information theory.’ ETH has other denominations, each nicknamed after the individual who contributed towards the project.