Optimism Token (OP) is an ERC20 token that grants specific governance rights within the Optimism Collective. The Optimism Collective, a new model of digital democratic governance, is comprised of companies, communities, and citizens committed to building a sustainable future for Ethereum and the world. OP is used to vote on project incentives, protocol upgrades, and treasury funds as part of the Collective’s “Token House” – one of two co-equal chambers tasked with balancing short-term incentives with Optimism’s long-term vision and growth. 

Launched in mid-2019, Optimism is an EVM equivalent Layer-2 (L2) scaling solution built on top of Ethereum (L1) that is faster and cheaper while inheriting the security properties of Ethereum. Optimism facilitates more efficient transactions through Optimistic Rollups, which allows multiple transactions to be compiled and settled on L2 before periodically submitting to the main Ethereum blockchain. OP has an initial supply of 4,294,967,296 tokens with a 2% annual inflation rate. 

More information here https://www.optimism.io/