Ethereum is a decentralized blockchain platform that enables the creation and execution of smart contracts, as well as the development of decentralized applications (dApps). It was proposed by Vitalik Buterin in late 2013 and launched in July 2015. Ethereum's native cryptocurrency is called Ether (ETH).

One of the key innovations of Ethereum is its ability to support Turing-complete smart contracts. Smart contracts are self-executing agreements with predefined rules and conditions. They automatically execute when the specified conditions are met, without the need for intermediaries or centralized control.

Ethereum introduced the concept of the Ethereum Virtual Machine (EVM), which is a runtime environment for executing smart contracts. The EVM allows developers to write smart contracts using various programming languages, with Solidity being the most commonly used language.

The Ethereum blockchain operates through a consensus mechanism called Proof-of-Work (PoW), similar to Bitcoin. However, Ethereum has been working on transitioning to a Proof-of-Stake (PoS) consensus mechanism called Ethereum 2.0 or Eth2. This upgrade aims to improve scalability, energy efficiency, and security on the Ethereum network.

The Ethereum blockchain has become the foundation for a vast ecosystem of decentralized applications, ranging from decentralized finance (DeFi) platforms and non-fungible tokens (NFTs) to gaming and decentralized exchanges. It has also facilitated the initial coin offering (ICO) boom, where numerous projects raised funds by issuing their own tokens on the Ethereum platform.

Ethereum's success has led to its widespread adoption and recognition as the second-largest cryptocurrency by market capitalization, after Bitcoin. Its open nature and programmability make it a popular choice for developers and businesses looking to build decentralized applications or leverage the power of smart contracts.