Sidechains Definition: A sidechain is a blockchain that is separate but attached to its parent blockchain. This connection is done using a two-way peg, which allows assets to interchange at a predetermined rate between the sidechain and the blockchain. While the original blockchain is considered the main blockchain, the sidechains are secondary, and often referred to as childchains.
When a parent or main blockchain sends coins to an address, which goes through security, then moves through the sidechains until the user can access them. Crypto coins can also move from the sidechain to the main blockchain.