Rollup
A scaling method that batches many transactions off-chain and posts a compressed proof or record to the base layer.
A rollup executes transactions away from the main chain, then rolls them into a single batch recorded on Layer 1. Compressed data is what makes it cheap. The base chain stores a summary instead of re-running every trade.
Two flavors exist. Optimistic rollups assume batches are valid and allow a challenge window; zk-rollups prove validity with cryptography upfront. Both borrow Ethereum's security because the data lives there.
The catch is the sequencer that orders transactions. Today that role is usually one company. Decentralizing it is the open problem.
Related terms
A rollup that assumes transaction batches are valid and lets anyone challenge fraud within a set dispute window.
zk-RollupA rollup that posts a cryptographic validity proof for every batch, giving near-instant finality on the base chain.
Layer 2A separate network built on top of a base chain to process transactions faster and far more cheaply.
Layer 1The base blockchain itself, where transactions settle and security lives, before any add-on networks built on top.