A mainnet is a fully developed and released version of a blockchain network. This stands in contrast with a testnet, which is generally used to perform tests and experiments on a blockchain before a mainnet is released. Testnets are used while a blockchain is live for experimentation and development as to not disrupt the main chain.
There are a few key phases that may occur before the mainnet stage. When a token sale is conducted, money may be used to fund the creation and testing of a product.
Once this phase has been successfully completed, the mainnet stage is usually moved forward. In this case, it implies that the blockchain is completely functional.
Once the initial coin offering (ICO) is finished, the mainnet will be deployed. In most cases, a native token will be used to represent this.
This is the following phase in the process and is known as the switch stage. On the blockchain, this is done via the exchange of tokens for new currencies.
Following the completion of the mainnet exchange, the new coins are often destroyed. This is done in order to ensure that only new coins are utilized rather than old coins.