Ether is the currency of Ethereum. Every activity on Ethereum that modifies its state costs Ether as a fee, and miners who are successful in generating and writing a block in a chain are also rewarded Ether. Ether can easily be converted to dollars or other traditional currencies through cryptoexchanges.
Ethereum has a metric system of denominations used as units of Ether. The smallest denomination or base unit of Ether is called wei. The following is a list of the named denominations and their value in wei which is available at https://github.com/ethereum/web3.js/blob/0.15.0/lib/utils/utils.js#L40:
var unitMap = { 'wei' : '1' 'kwei': '1000', 'ada': '1000', 'femtoether': '1000', 'mwei': '1000000', 'babbage': '1000000', 'picoether': ...
