Mainnet is the term used to describe when a blockchain protocol is fully developed and deployed, meaning that cryptocurrency transactions are being broadcasted, verified, and recorded on a distributed ledger technology (blockchain).
In contrast to mainnet networks, the term testnet describes when a blockchain protocol or network is not yet up and running on its full capacity. A testnet is used by programmers and developers to test and troubleshoot all the aspects and features of a blockchain network before they are sure the system is secure and ready for the mainnet launch.
In other words, a testnet only exists as a working prototype for a blockchain project, while a mainnet is a completely developed blockchain platform for users to send and receive cryptocurrency transactions (or any other kind of digital data that is recorded on a distributed ledger).
Usually, before the mainnet of a blockchain project is launched, the team will set up an Initial Coin Offering (ICO), an Initial Exchange Offering (IEO), or any other means that can help the project raise funds and grow their community. Typically, the collected funds are then used to develop the prototypes of the blockchain network, which is then tested during the testnet phase. After performing bug fixes and depending on the performance of the testnet, the team will then launch the mainnet version of the blockchain, which is (ideally) fully deployed and functional.
In 2017, many blockchain startups decided to perform ICO crowdfunding events. To do so, the majority of them chose to issue their own ERC-20 token on the ETHereum network. These tokens were then distributed to investors’ wallets, according to their contribution during the ICO phase.
After the ICO crowdfunding is complete and the blockchain is fully deployed, the team may release their mainnet, which will have their own native coin (on a proprietary blockchain) rather than the previously issued ERC-20 token. At this point, a process known as mainnet swap takes place, where the ERC-20 tokens are swapped for the coins of the new blockchain. After the mainnet swap is completed, remaining tokens are usually destroyed so that only the new coins can be used.
