Ethereum (ETH) is a decentralized, open-source blockchain platform launched in 2015 that introduced smart contracts and enabled the creation of decentralized applications (dApps). It transitioned from proof-of-work to proof-of-stake in 2022 (The Merge) and supports a massive ecosystem including DeFi, NFTs, stablecoins, and layer-2 scaling solutions for improved throughput and lower fees. ETH is used to pay for gas fees, stake for network security, and participate in governance, making it the backbone of programmable blockchain infrastructure.