What is Roll-Up?

Roll-ups are an off-chain aggregation of transactions inside a smart contract. Roll-ups are used to combine and process smart contract transactions off-chain before settling the final state on-chain. This is done to lower transaction fees given that the rising popularity of decentralized finance (DeFi) offerings has caused fees to increase substantially on some blockchain protocols. Roll-ups are considered a throughput solution, not a scaling solution, as they usually require additional hardware to settle transactions on-chain.