To a developer, I would liken the mainnet (main network) to the main branch of a Git version-controlled project, where the main branch represents code that is deployed to production.
In blockchain terms, this is the primary network or blockchain where real transactions are tracked.
For example you might test your smart contracts [↗] on a test blockchain like Goerli Testnet [↗] to ensure everything works as expected, then deploy your smart contract onto the Main Network to go live.
Here is another article you might like 😊 What Is Chain Linking?