Ether is the native cryptocurrency of the Ethereum blockchain.
Ethereum is the name of the blockchain platform, while ether is the asset used to pay transaction fees and computational costs on that network. Its commonly used ticker is ETH. Users and applications can transfer ether, and validators receive rewards denominated in ether under Ethereum’s proof-of-stake system.
Wei is not a separate cryptocurrency: it is the smallest denomination of ether, much as a satoshi is a small unit of bitcoin. Gwei is another denomination, commonly used when discussing gas prices; one gwei equals one billion wei. Ethereum’s network also hosts many tokens, but those tokens are distinct from ether and may follow standards such as ERC-20. This distinction between a blockchain’s native asset and tokens issued on it is a common source of confusion.