Optimistic Rollup
A layer 2 scaling method that processes transactions off-chain and posts summarized data to a main blockchain, assuming transactions are valid unless challenged.
An optimistic rollup is a layer 2 scaling system that helps a blockchain handle more transactions by moving most computation off the main chain while still relying on it for security. It bundles many transactions together, submits the transaction data or summary to the base chain, and “optimistically” assumes the batch is correct. If someone detects an invalid transaction, they can submit a fraud proof during a challenge period to dispute it.
This matters because optimistic rollups can reduce fees and increase throughput for apps such as decentralized exchanges, wallets, games, and payment systems, while keeping a strong connection to the underlying blockchain. The trade-off is that withdrawals back to the main chain may take longer because users must wait for the challenge window to pass. A practical comparison is a receipt at a store: the cashier processes many items quickly, and the receipt is accepted unless someone later checks it and finds a mistake.
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.