What is a Mainnet?
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 that participate in consensus, and all of the network transactions.
The mainnet is the most stable version of the network n,has passed testing procedures, such as stress tests, and gone through bug fixes and implementation improvements, and that require fixing, before being rolled out.
Blockchain updates are very different to upgrades being brought to a software or game, in the way they are deployed. The consensus (which are the fundamental rules which define who and how will get the next block in the chain) cannot be changed by a simple upgrade. It requires a hard fork. More on this later.
What is a Testnet?
The testnet is a replica of the blockchain network, implemented as a testing environment, and does not hold real-value. The biggest differences are the lack of value of the tokens that are being transacted on the testnet (the testnet tokens are just minted and then used for testing purposes, holding no real value), the miners and nodes do not work the same way they do on the mainnet (they are simulated), thus the entire validation is imitated, and last but not least, the dApps that are being deployed on the testnet are not interoperable at the same scale of the mainnet.
Testnets important purpose:: to test all the features of a network before considering the network to be stable. Testnets are used to mimic real-world environments to ensure implementations work as intended, and allow the broader community to start onboarding onto the network (especially for network maintainers and application developers), test different capabilities, and start to learn more about the network with the valuable experience gained on the testnet.
We learned about mainnet and testnet in this article, how they're different and how to properly use both environments.