Blockchain and Ethereum are related concepts, but they refer to different things. Here’s a breakdown of each:

### Blockchain
- Definition: A blockchain is a decentralized, distributed ledger technology that records transactions across many computers in such a way that the registered transactions cannot be altered retroactively. This ensures transparency and security.
- Structure: A blockchain consists of a chain of blocks, where each block contains a list of transactions. Each block is linked to the previous one, forming a secure chain.
- Types: There are various types of blockchains:
- Public Blockchains: Open to anyone (e.g., Bitcoin, Ethereum).
- Private Blockchains: Restricted access, used by specific organizations (e.g., Hyperledger).
- Consortium Blockchains: Controlled by a group of organizations.
- Use Cases: Beyond cryptocurrencies, blockchains can be used for supply chain management, voting systems, identity verification, and more.

### Ethereum
- Definition: Ethereum is a specific type of blockchain that enables developers to build and deploy decentralized applications (dApps) using smart contracts.
- Smart Contracts: These are self-executing contracts with the terms of the agreement directly written into code. They automatically execute actions when certain conditions are met.
- Ether (ETH): The native cryptocurrency of the Ethereum platform, used for transaction fees and as a form of payment within the ecosystem.
- Decentralized Finance (DeFi): Ethereum has become a leading platform for DeFi applications, allowing users to lend, borrow, and trade without intermediaries.
- NFTs: Ethereum is also the primary platform for non-fungible tokens (NFTs), which are unique digital assets representing ownership or proof of authenticity.

### Key Differences
- Scope: Blockchain is a broad technology; Ethereum is a specific implementation of blockchain technology with additional features like smart contracts.
- Functionality: While all blockchains can record transactions, Ethereum allows for complex programmable transactions through smart contracts.