The denomination used in defining the cost of gas in transactions involving Ether.
Gwei is a small unit of the Ethereum network’s Ether (ETH) cryptocurrency. A gwei or gigawei is defined as 1,000,000,000 wei, the smallest base unit of Ether. One gwei equals 0.000000001 or 10-9 ETH. Conversely, 1 ETH represents 1 billion gwei!
Gwei is a useful denomination to calculate gas fees (paid to miners for transaction processing) in a convenient way. Gwei also has the nickname “shannon,” for Claude Shannon, a mathematician and cryptographer referred to as "the father of information theory."
Ether (ETH) has other base units as well, each nicknamed after an important personality whose work has helped with the project in any way or form.
Here are a few:
1 wei (named for Wei Dai, a “godfather” of the crypto movement).
1 kwei (termed babbage after Charles Babbage) is equal to 10’3 wei.
1 mwei (termed lovelace after Ada Lovelace) is equal to 10’6 wei.
1 twei (termed szabo after Nick Szabo) equals 10’12 wei.
1 pwei (termed finney after Hal Finney) equals 10’15 wei.