Wei is the smallest denomination of ether, the cryptocurrency used on the Ethereum network.
As the prices of various cryptocurrencies, including ether, skyrocketed in 2017, transaction sizes have become smaller.
To accurately denote the number of transactions that may appear to be a very small fraction of ether but of high value when converted to US dollars or other real-world currencies, new units have been created to define and accurately support transactions.
Wei is named after Wei Dai, a crypto activist who is known for supporting extensive use of strong encryption technologies and security-oriented.
1 Ether (ETH) = 1,000,000,000,000,000,000 Wei (1018)