Optimism

Optimism is a layer 2 blockchain that helps Ethereum to scale, by processing a bunch of transactions on its blockchain and posting them in batches on Ethereum providing fast speed and low fees. It is designed so that users can send arbitrary messages between smart contracts on Optimism and Ethereum. This makes it possible to transfer assets, including ERC20 tokens, between the two networks.

Overview

Optimism is a layer-two blockchain for Ethereum using optimistic rollups as scaling technology. It is one of Ethereum’s biggest scaling solutions with over $250 million in TVL at the time of writing. Optimistic rollups outsource the execution of transactions to a L2 solution like Optimism.
The transactions on Optimism are rolled up into batches that get relayed to the Ethereum mainnet, which only records the new chain state. Since their validity is assumed, the rollups are called optimistic. A rollup's validity can be challenged for up to seven days, which is why withdrawals from Optimism to Ethereum take seven days.