A parent chain is the primary blockchain in a network, while sidechains are parallel blockchains connected to the parent chain. Sidechains function by locking value in the parent chain and transferring it to a separate distributed ledger. For instance, in the case of Bitcoin, funds are locked in a designated Bitcoin address, and once confirmed by the network, a message is sent to the sidechain indicating that new tokens can be distributed based on the locked funds.
The main benefit of sidechains is that they can increase transaction speed. Before moving the value back to the parent chain for further usage, they permit some transactions to be completed in particular contexts, such as a single store or game. This is comparable to a parent assigning homework to a child, who then completes it at home and brings it back to the parent, who then distributes it to the appropriate parties.
Scaling slower cryptocurrencies like Bitcoin has been addressed with the use of sidechains. The concept is to use sidechains for smaller transactions involving very little amounts of cryptocurrency and reserve the main blockchain for larger transactions. With the help of this strategy, Bitcoin will be presented as a more useful currency that can be used for regular activities like buying