Mainnet
In short A mainnet is the live version of a blockchain, where fees are paid in real coins and tokens carry real value, unlike a testnet.
A mainnet is the live version of a blockchain, the one where transactions have real economic consequences and tokens carry real value. Ethereum, Solana, BNB Chain, and Base each run a mainnet. When someone says a token is on Solana, they mean Solana's mainnet unless they say otherwise.
Mechanically, a mainnet is a network of nodes and validators that agree on the order of transactions and record them in blocks. Fees are paid in the chain's native coin, such as ETH, SOL, or BNB. Once your transaction is included in a block, no support team can undo it for you. Confirmation is not the same as finality, though. On many chains a recently confirmed transaction can still be dropped by a chain reorganization, and it only becomes effectively permanent after more blocks or an explicit finalization step. In rare cases, such as a major hack, a community has coordinated a rollback or fork, but you should never count on that.
A testnet is the contrast case. It runs similar software, but its coins are handed out free by faucets and are normally not meant to have any monetary value, so developers can experiment without risk. Anyone can deploy a token on a testnet under any name, including a copy of a real ticker. When a project says it is deploying to mainnet, it means its contracts or its own chain are moving into production use, handling real funds. That does not mean the code is bug-free, and a launch from another chain often involves a token swap or migration.
Before you send or approve anything, confirm which network your wallet is set to. Many EVM chains share the same address format, so funds sent on the wrong network can be hard or impossible to recover. Take the contract address from the project's official site or verified channels, cross-check it in a block explorer for the correct chain, and be skeptical of addresses pasted in chats or screenshots.
A live mainnet does not make a token safe. The chain can work perfectly while a token's contract is a scam, and copycat tokens with identical names and tickers exist on mainnet too. Be wary of projects that keep pushing back a mainnet date while selling tokens in the meantime, since a sale before any working network exists is a bet on a promise.