Ethereum is a "blockchain app platform", and a "world
computer".
It has Ether as a volatile cryptocurrency, with the ticker ETH. The price of ETH drops when Ethereum hodlers read news headlines
like "The founder of Ethereum died in a car
crash", or there are scams with initial token offerings, or ITOs. The network slows down during ITOs, or when apps are used too much, such as when too many
people play a
game for trading digital
cats, called Cryptokitties.
It's "a decentralized platform that runs smart contracts: applications that run exactly as programmed without any possibility of downtime, censorship, fraud or third-party interference.
"These apps run on a custom built blockchain, an enormously powerful shared global infrastructure that can move value around and represent the ownership of property.
"This enables developers to create markets ... and many other things ... all without a middleman or counterparty risk.
The project was bootstrapped via an Ether ICO in
August 2014.
Developers and researchers are working on various improvements improvements to the protocol and ecosystem, e.g. as described in a thread on ethresear.ch.