Sidechains
A sidechain is a separate blockchain connected to a main chain by a bridge, with its own consensus and security.
In depth
Assets move to the sidechain, are used there with different rules or lower fees, and can be moved back. Unlike rollups, a sidechain does not inherit the main chain’s security — if its validators are compromised, so are the bridged assets. Polygon PoS began as an Ethereum sidechain.
Why it matters
The security difference between sidechains and rollups matters when choosing where to hold assets.