What is Optimism (Ethereum Scalability Stack)?

Optimism is an application designed to operate inside of the Ethereum network to increase Ethereum's scaling and transaction throughput via Optimistic Rollup (OR) technology. ORs are a specialized scaling solution designed to make transactions on the Ethereum network more efficient, faster, and cheaper. Optimism makes use of the Optimistic Virtual Machine (OVM) to facilitate Ethereum Virtual Machine (EVM) integration to allow developers to write scalable smart contracts on Ethereum. Not to be confused with a sidechain, Optimism lives inside the Ethereum network as a series of smart contracts that have the ability to execute Ethereum transactions.