Optimistic Rollups are a layer 2 scaling solution for blockchains, primarily used to enhance the transaction speed and reduce costs. They work by processing transactions off the main blockchain, bundling them together, and then submitting a summary back to the main chain. This allows for more transactions to be handled simultaneously, improving overall efficiency. In Optimistic Rollups, the term "optimistic" refers to the assumption that transactions are valid by default. If someone believes a transaction is fraudulent, they can challenge it within a specific time frame. This mechanism helps maintain security while allowing for faster processing of transactions.