A Layer 2 blockchain for Ethereum. Launched in 2021, Optimism is an optimistic rollup chain, which accumulates transactions and summarizes them with a cryptographic proof on Ethereum. The "optimism" means that people are assumed to be honest, but the transactions can be challenged. If fraud is detected, a "fraud proof" can be published, and if found valid, the transaction can be withdrawn within a certain time period. Thus, regular withdrawals are delayed approximately one week in case there is a dispute.
True to its advantage as a Layer 2 blockchain, Optimism executes transactions faster, and fees are lower than Ethereum. OP is the native token. See
Layer 2 blockchain and
OP Stack.
Contrast with zk-Rollups
zk-Rollups are another form of rollup used on Layer 2 blockchains (see
zero-knowledge proof).