Ethereum is a decentralized, open-source blockchain platform that enables the creation and execution of smart contracts. It was proposed by Vitalik Buterin in late 2013 and launched in July 2015. Ethereum introduced the concept of a programmable blockchain, allowing developers to build decentralized applications (DApps) and tokens using its native programming language, Solidity.

The Ethereum blockchain is designed to support a wide range of applications beyond simple financial transactions. Smart contracts are self-executing agreements with the terms of the agreement directly written into code. They automatically execute when predefined conditions are met, providing transparency, security, and eliminating the need for intermediaries.

Ethereum's native cryptocurrency is called Ether (ETH), which is used as a medium of exchange within the network. Ether can also be used to pay for transaction fees and computational services on the platform. Additionally, Ethereum introduced the concept of ERC-20 tokens, which are fungible tokens built on the Ethereum blockchain. These tokens can represent assets, currencies, or even voting rights within decentralized applications.

One of the defining features of Ethereum is its ability to create and support decentralized autonomous organizations (DAOs). DAOs are organizations run by smart contracts, where decisions are made through voting mechanisms, and funds are managed transparently and collectively by the participants.

Ethereum has undergone several major upgrades throughout its history. The most significant upgrade to date is Ethereum 2.0, also known as ETH2 or Serenity. This upgrade aims to improve scalability, security, and sustainability by transitioning from a proof-of-work (PoW) consensus mechanism to a proof-of-stake (PoS) consensus mechanism.

Ethereum has become a prominent platform for blockchain-based development, hosting thousands of decentralized applications, including decentralized finance (DeFi) protocols, non-fungible token (NFT) marketplaces, and various other innovative projects.

Please note that the information provided here is based on the knowledge available up until September 2021, and there may have been further developments or updates to the Ethereum blockchain since then.