Binance Smart Chain (BSC) is a fork or modified copy of the Ethereum network. BSC has a different consensus mechanism and network parameters that allow it to have lower transaction costs and faster processing time.
BSC is Ethereum compatible, meaning that your wallet address on Ethereum is the same as on BSC. Assets can be moved back and forth between BSC and Ethereum using a “bridge”.
You can read more about BSC in the official blog.