Glossary
Testnet
A test instance of a blockchain — same client software as mainnet but with valueless native tokens — used to deploy and try contracts before going live.
Testnets like Sepolia and Holesky run the same client software as mainnet but with their own validators, their own state, and their own native asset that you can pull from a faucet for free.
They let you deploy contracts, simulate user flows, and verify upgrades without spending real money. Each testnet has its own intended lifecycle and may be deprecated as new ones come online — Goerli, Kovan, Rinkeby, and Ropsten have all been retired in Ethereum's history.