Rollup

A rollup is a layer 2 network that executes transactions off the main chain (layer 1) and then periodically posts a compressed state commitment—along with the underlying transaction data—back to it, so the rollup's state can always be reconstructed and verified from layer 1 alone. L2BEAT, the leading tracker of these networks, defines rollups as systems whose state commitments are "validated by either Validity Proofs or... accepted optimistically and can be challenged via [a] Fraud Proof mechanism," which is exactly the split between ZK rollups and optimistic rollups. Because the data lands on the base chain, a rollup inherits its parent chain's security rather than depending on a separate validator set the way a sidechain does. Arbitrum, Optimism, Base, zkSync, and Starknet are all rollups built on Ethereum. For tokenized domains, rollups are what make routine actions—transfers, DNS updates, sub-domain issuance—affordable, since executing off the base chain can cut fees by 10–100x.