The version of a protocol that uses real money. A cryptocurrency is generally considered to be “live” after the first Mainnet block (the genesis block) is mined.

When a blockchain project is complete and it’s developers have deployed it -- that means it becomes a mainnet. The mainnet will be processing cryptocurrency transactions, each one being broadcast, verified, and recorded. 

When you’re using a blockchain that’s new, make sure it’s a mainnet network and not a testnet -- which describes when a blockchain network is not yet up or not yet up to its full capacity. A testnet is used by programmers and developers, hopefully before launch. They use a testnet to test and troubleshoot all the aspects and features before they secure the blockchain and ready it for the mainnet launch.

A testnet should only exist as a working prototype and should not be used to send anything valuable. A mainnet is a completely developed blockchain platform and can be used to send and receive cryptocurrency transactions or smart contracts or other information that requires that specific blockchain protocol. 

You may have encountered a testnet if the team set up an Initial Coin Offering (ICO), an Initial Exchange Offering (IEO), or any other ways of raising funds and growing their community. 

These days a testnet may be available for users to show the seriousness of the project and help collect more funds to turn this prototype into a proper blockchain network, which is then tested during the testnet phase again just to make sure. 

If you’re using a testnet and waiting for the mainnet, don’t be discouraged as the team takes time to patch bug fixes and improve performance of the testnet. Sooner or later the team will then launch the mainnet version of the blockchain/

Generally the native coin (on a proprietary blockchain) will take over any previously issued ERC-20 tokens used during the crowdsale and fundraising. At this point, a process known as mainnet swap should take place for you. So keep your eyes for such an event where the ERC-20 tokens are swapped for the coins of the new mainnet blockchain. If this happens then the coins from testnet are usually destroyed so that only the new coins will be used by investors and users and not make anyone confused by anything.