Sidechain

An independent blockchain that runs parallel to a main chain (the 'parent chain') and is connected to it via a two-way bridge, allowing assets to move between both chains. Sidechains have their own consensus mechanisms and validators, offering different performance and cost trade-offs than the parent chain. Unlike Layer 2 rollups, sidechains do not inherit the parent chain's security — they are responsible for their own security guarantees. Polygon PoS (before its transition to a ZK validium) was a well-known Ethereum sidechain.