Ethereum is an open-source, decentralized blockchain platform that was launched in 2015. It was created by Vitalik Buterin and a team of developers with the goal of enabling the development of decentralized applications (DApps) and smart contracts.

Unlike Bitcoin, which is primarily a digital currency, Ethereum's main focus is on providing a platform for building decentralized applications. It introduced the concept of smart contracts, which are self-executing contracts with the terms of the agreement directly written into lines of code. These smart contracts can automatically facilitate, verify, and enforce the negotiation or performance of an agreement without the need for intermediaries.

Ethereum has its own cryptocurrency called Ether (ETH), which is used to facilitate transactions and incentivize participants on the network. Ether is also used to pay for computational services, or "gas," required to execute smart contracts and deploy DApps on the Ethereum blockchain.

One of the key features of Ethereum is its ability to support the creation of new tokens and assets on its blockchain. This has led to the development of numerous Initial Coin Offerings (ICOs) and token sales, as well as the emergence of various other cryptocurrencies and digital assets built on the Ethereum platform.

In terms of technology, Ethereum initially used a proof-of-work (PoW) consensus algorithm similar to Bitcoin. However, it is in the process of transitioning to a proof-of-stake (PoS) consensus algorithm called Ethereum 2.0. This upgrade aims to improve scalability, security, and energy efficiency.

Ethereum has a large and active developer community, and it has become the most widely used platform for building decentralized applications. It has also gained popularity for its ability to support decentralized finance (DeFi) applications, non-fungible tokens (NFTs), and other innovative use cases within the blockchain ecosystem.