Mainnet, short for main network, is the term used to denote the final phase of development of a blockchain network. The mainnet of a blockchain is launched after the testnet (test network), where developers add new functionalities, test them, and rectify any issues.
The completely live version of a blockchain ready for commercial use is known as the mainnet version. The blockchain’s mainnet can execute real transactions, supporting the transfer of data and assets on its infrastructure and storing information accessible by all network participants.
The mainnet version is the live, independent version of the blockchain protocol, which is wholly developed and rolled out to support real-world applications. This is in contrast to a testnet version which could usually operate on top of another blockchain network and is a work in progress against the completed, ready-to-use, and live version that is the mainnet.