Ethereum is a decentralized blockchain platform that enables the creation and execution of smart contracts and decentralized applications (dApps). It was proposed by Vitalik Buterin in 2013 and launched in 2015.

The Ethereum blockchain is known for its programmable functionality, allowing developers to build and deploy smart contracts. Smart contracts are self-executing agreements with predefined conditions, which automatically execute once those conditions are met. They facilitate the exchange of digital assets, tokens, or other forms of value in a transparent and secure manner, without the need for intermediaries.

One of the key features of Ethereum is its native cryptocurrency called Ether (ETH). Ether serves as the fuel or "gas" that powers the execution of smart contracts and allows users to participate in the Ethereum network. It is also traded on various cryptocurrency exchanges.

Ethereum introduced the concept of ERC-20 tokens, which are fungible tokens built on the Ethereum blockchain. These tokens follow a common set of rules, making them easily interchangeable and compatible with different applications and wallets. ERC-20 tokens have played a significant role in the growth of initial coin offerings (ICOs) and the tokenization of various assets.

However, Ethereum has faced scalability challenges due to its design. As more applications and users joined the network, it became congested and faced high transaction fees and slower confirmation times. To address these issues, Ethereum has been working on a major upgrade called Ethereum 2.0 or ETH2, which aims to transition the network from a proof-of-work (PoW) consensus mechanism to a proof-of-stake (PoS) mechanism. This upgrade is being implemented in multiple phases and is expected to enhance scalability, security, and energy efficiency.

The Ethereum blockchain has also been a catalyst for the development of decentralized finance (DeFi) applications. DeFi refers to a range of financial services and applications that operate on a decentralized infrastructure, often built on Ethereum. These include lending platforms, decentralized exchanges, stablecoins, and yield farming protocols, among others.

It's worth noting that while Ethereum is the most well-known and widely used blockchain platform for smart contracts, there are other blockchain platforms that offer similar functionalities, such as Binance Smart Chain (BSC), Polkadot, and Cardano. These platforms differ in terms of their consensus mechanisms, scalability solutions, governance models, and developer ecosystems.