Görli is an Ethereum testnet (or test network). Testnets are typically used by developers to run "tests" for their application or software. Currency on testnet are valueless. Görli is open-source and is the first proof-of-authority cross-client testnet, synching Parity Ethereum, Geth, Nethermind, Pantheon, and EthereumJS.
Visit the official website here: https://goerli.net