Ethereum’s currency unit is called ether, identified as ETH, and is divided into units. The smallest unit possible is named wei. One ether is one quintillion wei, namely 1,000,000,000,000,000,000.
Denominations of cryptocurrencies may help describe small-value transactions, especially regarding small amounts of ETH typically used for transaction fees or when setting the gas limit of a transaction.
Wei is the smallest unit of ether, like satoshi, which is to bitcoin or pennies to pounds and cents to dollars/euros. One ether corresponds to 1018 ether or 1,000,000,000,000,000,000.
Ether’s various denominations also have a colloquial name that pays homage to many of the great minds of computing and cryptography. For example, wei stands for Wei Dai, a cryptography activist known for supporting the widespread use of strong cryptography and privacy-oriented technologies.
Although Wei is the smallest ETH denomination, it is currently not the most commonly used unit for Ethereum transactions. Gwei -which represents one million wei- has become the default denomination for referring to gas fees on the Ethereum blockchain.