Optimistic rollups are a layer 2 solution to the scalability problem. According to Vitalik, they are a central part of the future Ethereum network.
Basically, it allows doing expensive calculation off-chain, with data stored on-chain to verify that the calculation was run correctly. If calculation was not done correctly, it will be reverted and the node that did it may lose some stake.
It will allow up to x100 scalability on throughout, meaning that we will probably do away with expensive fees in a few months when it’s widely used.
It’s a major breakthrough, and I think this news deserves more love. ZK rollups are the next step and need more work to be fully available. It’s amazing technology.
More details on this link : https://vitalik.ca/general/2021/01/05/rollup.html