Ether is the internal network currency for Ethereum. Just like Bitcoin has Satoshi and Millibits and the USD has dollars and cents, Ethereum has its own denominations and naming terminology. Ether is also used to pay for various transaction and computational tasks performed on the Ethereum network – and this is confusingly called GAS. There is a GAS limit on each block (i.e. how many computational transactions can be performed per block) which limits the block size and determines the cost of executing a contract immediately. A table below shows the different Wei denominations:
All the small denominations are named after pioneers in the Cryptographic space in a nod to Bitcoin’s naming terminology. A Finney is named after Hal Finney and a Szabo after Nick Szabo, some of the usual suspects for the face behind the eponymous Satoshi Nakomoto.