GETH is a token used in the Goerli testnet. Goerli is a testnet that combines both a PoA consensus mechanism with wider support of node software compared to Rinkeby and Kovan. Goerli supports both Geth and Parity as well as Nethermind and Hyperledger. With this higher level of support, the popularity of Goerli has been increasing. It is also the first testnet that was attempted to be moved to the proof-of-stake mechanism before running into issues after multiple attempts.

Testnet tokens are a test currency that allows you to test your Ethereum application before going live on mainnet. Testnet tokens can be used in place of mainnet Ether tokens on testnets like Goerli.