Ether is the cryptocurrency of Ethereum. The two terms are frequently confused, so it is important to remember, Ethereum is the system and technology, and Ether is its currency.
If you want to do things on the Ethereum system, you will needs some Ether. Small bits of Ether fuel the transactions. These small bits that fuel the system are referred to as ‘gas’. Each transaction on Ethereum needs a certain amount of ‘gas’ to complete the transaction. The bigger the job, the more gas needed.