Sidechain
A separate blockchain connected to a main blockchain, allowing assets or data to move between them while using its own rules and security model.
A sidechain is an independent blockchain that runs alongside a main blockchain, such as Bitcoin or Ethereum, and is connected to it through a bridge or two-way peg. This connection lets users move assets from the main chain to the sidechain, use them there, and later move them back. Unlike a typical layer 2 rollup, a sidechain usually has its own validators, consensus rules, block production, and security assumptions rather than directly inheriting the full security of the main chain.
Sidechains matter because they can offer lower fees, faster transactions, or specialized features without changing the main blockchain itself. They are often used for payments, games, DeFi apps, or experiments that need more flexibility than the base layer provides. For example, Polygon PoS is commonly described as a sidechain-style network connected to Ethereum, where users can bridge tokens over and interact with apps at lower cost. The trade-off is that users must trust the sidechain’s bridge and validator system, so risks can differ from using the main chain directly.
Other terms in Layer 2 & Scaling
Data Availability
The assurance that the transaction data needed to verify a blockchain or layer 2 network can be accessed by anyone who needs it.
Fraud Proof
A fraud proof is evidence submitted to a blockchain to show that a proposed transaction result or rollup state is invalid.
Layer 2
A Layer 2 is a secondary network or protocol built on top of a blockchain to process transactions faster and cheaper while relying on the main chain for security.
Layer 3
A Layer 3 is an application-specific blockchain layer built on top of a Layer 2 to add customization, scalability, or specialized features.