What is Mainchain?

A mainchain is a term used to describe the main, Layer-1 network of a blockchain network protocol such as Bitcoin or Ethereum. The name 'mainchain' generally means it is the most powerful blockchain and most important blockchain network within a specific blockchain ecosystem. Generally, other blockchain protocols and decentralized applications are built 'on top of' the mainchain. As an example, many of the most prominent decentralized finance (DeFi) projects are constructed to run on top of the Ethereum network's mainchain.