The mainchain is the primary layer of a blockchain architecture where every transaction is processed and finalized. Applications and sublayers are built on top of the mainchain. It adds security and privacy and improves decentralization to the whole ecosystem.

How Does a Mainchain Work?

The mainchain, often referred to as the parent blockchain, is the original backbone of the entire blockchain network. It connects all the blocks around the network and stores the record of transactions. Once data is stored on the blockchain, it is impossible to change it. 

Primary blockchains often get burdened and slow down due to heavy traffic. That is how the concept of secondary layers was introduced. Secondary layers are intermediaries between the main blockchain and the decentralized apps (DApps), allowing users to carry out processes through them. Still, the final settlement of every transaction of the network occurs on the mainchain exclusively. An excellent example of a secondary layer is the Lightning Network of the Bitcoin blockchain. It enables speedy transactions between relevant wallets. However, all transactions on this layer must be finalized on the Bitcoin mainchain to be considered complete.

source: coinmarketcap