Ether is the main cryptocurrency associated with the Ethereum blockchain; each of the contract accounts can create their own currency, but Ether is used within the Ethereum blockchain to pay for the execution of the contracts on the EVM. Ether is used for purchasing gas, and the smallest unit of Ether is used as the unit of gas.
Since Wei is the smallest unit of Wei, here is a table, listing the denominations and the name commonly used for them, along with the associated value: