Glossary
Optimistic Rollup
A Layer-2 that posts L2 blocks to L1 and assumes they are valid, allowing anyone to challenge them with a fraud proof during a withdrawal window.
An optimistic rollup batches L2 transactions, computes the new state, and posts the result to L1. The rollup is "optimistic" because the L1 contract takes the state at face value — unless, during a challenge window (typically seven days), someone submits a fraud proof showing the state transition was invalid.
Withdrawals back to L1 wait for that window to close, which is why L2-to-L1 transfers on optimistic rollups take a week unless you use a liquidity-provider bridge that fronts you the funds.