This definition comes from the technical glossary.
A global testing environment in which developers can obtain and spend duffs that have no real-world value on a network that is very similar to the Dash mainnet.
Devnet (a public or private development network which mimics mainnet)
Regtest (a local testing environment where developers can control block generation)
Testnet mode — Developer Examples
Testnet — Bitcoin Wiki
Get testnet dash (Dash.org) — Testnet Faucet
Get testnet dash (Masternode.io) — Testnet Faucet
Get testnet dash (Dashninja.pl) — Testnet Faucet