The mainnet is the primary network where actual transactions take place in a blockchain ecosystem. Contrasted with testnets (test networks), which are used for testing purposes and do not involve real monetary value, mainnets facilitate live functionalities and support decentralized applications (dApps). Once a project moves from a testnet to a mainnet, it indicates the product is ready for real-world use and is available for the public to interact with using real currency or assets.