Ethereum is a decentralized, open-source blockchain system that enables the creation and execution of smart contracts and decentralized applications (DApps). It was proposed by Vitalik Buterin in late 2013 and development was crowdfunded in 2014, with the network going live on July 30, 2015. Ethereum's native cryptocurrency, Ether (ETH), is used to facilitate transactions and incentivize participants to secure the network through a process called mining or staking, depending on the network's consensus mechanism.

One of Ethereum's key innovations is its ability to execute smart contracts, which are self-executing contracts with the terms of the agreement written directly into code. These contracts run on the Ethereum Virtual Machine (EVM), which is capable of executing code of arbitrary algorithmic complexity. This functionality enables developers to build decentralized applications across various industries, including finance, gaming, supply chain management, and more.

Ethereum also introduced the concept of decentralized autonomous organizations (DAOs), which are organizations governed by smart contracts and run by code rather than traditional centralized management structures.

Overall, Ethereum has played a significant role in advancing blockchain technology and enabling the development of a wide range of decentralized applications and innovative use cases.