Features

Optimism uses a technology called rollups, specifically Optimistic rollups.

They’re called rollups because they roll up (or bundle) the data about hundreds of transactions – non-fungible token (NFT) mints, token swaps … any transaction! – into a single transaction on Ethereum mainnet (layer 1). When so many transactions are rolled up into a single transaction, the blockchain transaction, or "gas," fee required to pay comes down to only one transaction, conveniently distributed across everyone involved.

And they’re called Optimistic rollups because transactions are assumed to be valid until they are proven false, or in other words, innocent until proven guilty. There’s a time window during which potentially invalid transactions can be challenged by submitting a “fraud proof” and running the transactions’ computations with reference to available state data. Optimism reimburses the gas needed to run the computation of the fraud proof.