The Ethereum Blockchain1

The Ethereum Blockchain is an evolution of the Bitcoin blockchain protocol, the first release of the protocol was in 2015 and it evolved a lot since then. The intent of Ethereum is to create an alternative protocol for building decentralized applications, providing a different set of tradeoffs that are very useful for a large class of decentralized applications, with particular emphasis on situations where rapid development time, security for small and rarely used applications, and the ability of different applications to very efficiently interact, are important. Ethereum does this by building what is essentially the ultimate abstract foundational layer: a blockchain with a built-in Turing-complete programming language, allowing anyone to write smart contracts and decentralized applications where they can create their own arbitrary rules for ownership, transaction formats and state transition functions. Smart contracts, cryptographic "boxes" that contain value and only unlock it if certain conditions are met, can also be built on top of the platform, with vastly more power than that offered by Bitcoin scripting because of the added powers of Turing-completeness, value-awareness, blockchain-awareness and state.

1: https://github.com/ethereum/wiki/wiki/White-Paper