Ether is covered in full in the entry Ethereum (ETH), which explains the coin's history, supply, uses and market. The network itself, its architecture and its upgrades are described separately under Ethereum Blockchain. This page gives a short definition and explains why the names are often mixed up.
Ether, ticker ETH, is the native cryptocurrency of Ethereum. Every transaction and smart-contract action on the network is paid for in ether through gas fees, part of which has been burned since the EIP-1559 reform of 2021. Since Ethereum moved to proof of stake in 2022, validators must lock up ether as a security deposit, and they earn new ether and fees in return. Ether is also widely used as collateral in decentralized finance and as a trading pair for other tokens. Its smallest unit is the wei, and one ether equals wei; fees are commonly quoted in gwei, a billion wei.
In everyday speech, people often say "Ethereum" when they mean the coin, but strictly Ethereum is the network and ether is its currency, much as a country and its money have different names. This site therefore keeps the coin under its market name, Ethereum (ETH), and the network under Ethereum Blockchain, while tokens built on the network follow standards such as ERC-20.