Ethereum is a world computer running on nodes distributed worldwide. It runs on a blockchain secured by miners executing a Proof of Work consensus algorithm, with plans to move to a Proof of Stake consensus algorithm.
Ether (ETH) is the currency which is used to run smart contracts on the Ethereum platform.
Ethereum provides the Ethereum Virtual Machine (EVM) a decentralized Turing-complete virtual machine. “Gas”, an internal transaction pricing mechanism, is used to mitigate spam and allocate resources on the network.
Ethereum was proposed by Vitalik Buterin in 2013 and the public network went live in in July 2015.
The average blocktime in Ethereum is about 15-20 seconds.