Optimism is a Layer 2 scaling solution for Ethereum, designed to improve transaction throughput and reduce fees by utilizing optimistic rollups. It achieves faster and cheaper transactions by batching multiple transactions off-chain and submitting them as a single batch to the Ethereum mainnet, while maintaining security through a fraud-proof mechanism. Unique for its compatibility with existing Ethereum smart contracts, Optimism aims to enhance the usability and scalability of the Ethereum ecosystem.