Rollup

A rollup is a layer-2 network that executes transactions off the main chain, then posts compressed data and evidence of correctness back to layer 1, which remains the settlement and security anchor. Because thousands of transactions share the cost of a single layer-1 posting, fees fall sharply while users keep the ability to exit to the base chain. Two families dominate: optimistic rollups, which assume batches are valid and rely on fraud proofs during a challenge window, and ZK rollups, which submit validity proofs up front. Practical things to check before using one are who operates the sequencer, whether you can still withdraw if that operator disappears, where transaction data is published, and who controls contract upgrades.