Ethereum (ETH) is a decentralized, open-source blockchain platform that enables the creation and execution of smart contracts and decentralized applications (DApps). Launched in 2015 by programmer Vitalik Buterin, Ethereum has become the second-largest cryptocurrency by market capitalization, after Bitcoin.

While Ethereum shares some similarities with Bitcoin, such as utilizing a decentralized ledger to record transactions, its primary focus is on enabling developers to build and deploy DApps and smart contracts. Smart contracts are self-executing contracts with the terms of the agreement directly written into code, allowing for trustless and automated transactions.

Ethereum uses a native cryptocurrency called Ether (ETH) as the fuel for executing smart contracts and for conducting transactions within the network. Users pay transaction fees in Ether, known as "gas," to compensate miners for validating transactions and adding them to the blockchain.

In its early days, Ethereum utilized a Proof-of-Work (PoW) consensus mechanism similar to Bitcoin. However, Ethereum is transitioning to a more energy-efficient Proof-of-Stake (PoS) mechanism called Ethereum 2.0, which aims to improve scalability, security, and sustainability. The Ethereum platform has given rise to numerous decentralized finance (DeFi) applications, non-fungible tokens (NFTs), and other innovative use cases, making it a popular choice for developers and investors alike.