A mainnet blockchain network is a stable, production-ready, and live version of a blockchain network with real value. It hosts all the network maintainers participating in consensus and all network transactions.
Mainnet is the most stable version of the network that has passed testing procedures, such as stress tests, and gone through bug fixes and implementation improvements before being rolled out.
Blockchain updates are very different from upgrades being brought to software or games in how they are deployed. A simple upgrade cannot change the consensus (the fundamental rules that define how and who will get the next block in the chain). This requires a hard fork. More on this later…
Testnets are blockchain network clones created for developers to run, test, and debug their projects in a real-world environment to be able to document their performance before launching to mainnet. The testnet environment mimics the functionality of a blockchain network.
Testnets are not usually open to the public and don’t hold any real value cryptocurrency. For testing purposes, testnets use “fake money” testnet tokens that you can collect through a testnets faucet that don't have any real value.
What’s the importance of Testnet?