Rollup
A Layer 2 that processes transactions off-chain in bulk, then posts compressed proof to the base chain — Ethereum's core scaling strategy.
A rollup executes many transactions on a separate Layer 2 chain, bundles (“rolls up”) them, and posts compressed data plus a proof back to the base Layer 1. It inherits the L1’s security for settlement while multiplying throughput and slashing per-transaction fees. Rollups are the centerpiece of Ethereum’s “rollup-centric roadmap.”
Two families exist: optimistic rollups assume transactions are valid and allow challenges, while zk-rollups prove validity cryptographically upfront. Both let Ethereum scale without every node re-executing every transaction. The nuance worth knowing: rollups vary in maturity, and many still run centralized components (sequencers, upgrade keys), so “inherits L1 security” is a spectrum, not a binary.