> Ethereum is a decentralized, open-source blockchain with smart contract functionality. Ether (ETH) is the native cryptocurrency of the platform. It is the second-largest cryptocurrency by market capitalization, after Bitcoin. Ethereum is the most actively used blockchain.

It's a blockchain whose token wasn't intended as a cryptocurrency but as a medium for paying for having a program ("smart contract") stored on it run on every node of the network. In practice this can be used for all sorts of things, including bootstrapping the vast majority of other cryptocurrencies currently in existence, but under the current system it can't process transactions effectively enough to be useful in that manner.

As I understand it Ethereum 2, which is a really long term thing they've been doing for years, is meant to gobble up the original Ethereum completely once all stages of deployment are completed (any prior forks that may happen would remain independent, I guess).