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's native cryptocurrency is called Ether (ETH).

Here are some key aspects of the Ethereum blockchain:

Smart Contracts: Ethereum allows developers to create and deploy smart contracts, which are self-executing agreements with predefined rules and conditions. Smart contracts are written in Solidity, a programming language specifically designed for Ethereum.

Decentralization: Ethereum is a decentralized network, meaning it operates on a peer-to-peer basis without relying on a central authority. The blockchain is maintained by a network of nodes spread across the globe, which participate in the validation and verification of transactions.

Ethereum Virtual Machine (EVM): The Ethereum Virtual Machine is a runtime environment that executes smart contracts. It enables developers to build decentralized applications (DApps) that run on the Ethereum network. The EVM ensures the execution of smart contracts is consistent across all nodes.

Gas: Gas is the unit used to measure the computational effort required to process transactions and execute smart contracts on the Ethereum network. Gas fees are paid by users to incentivize miners and nodes to process their transactions. The cost of gas can vary depending on the complexity and demand on the network.

Proof of Stake (PoS): Ethereum is transitioning from its current consensus mechanism, Proof of Work (PoW), to a PoS consensus mechanism called Ethereum 2.0. PoS will replace miners with validators who will secure the network and validate transactions based on the amount of ether they hold and are willing to "stake."

Ethereum Improvement Proposals (EIPs): EIPs are proposals for changes and improvements to the Ethereum protocol. They can introduce new features, improve security, or address other issues. EIPs go through a review process and community consensus before being implemented.

Ethereum has gained popularity due to its ability to support the development of decentralized applications, initial coin offerings (ICOs), and the creation of new tokens and digital assets through its ERC-20 and ERC-721 token standards. It has also become a platform for decentralized finance (DeFi) applications, allowing users to engage in lending, borrowing, and trading activities without intermediaries.

It's important to note that the information provided here is based on the knowledge available up until September 2021, and there may have been updates or changes to the Ethereum blockchain since then.