Layer-2 solutions are technologies built on top of a blockchain, like Ethereum, to improve its scalability and transaction speed. They help reduce congestion on the main network by processing transactions off-chain, which means outside the main blockchain. This allows for faster and cheaper transactions while still benefiting from the security of the underlying blockchain. Common examples of layer-2 solutions include State Channels and Rollups. State Channels allow users to conduct multiple transactions privately before settling on the main blockchain, while Rollups bundle many transactions together, reducing the amount of data that needs to be processed on the main chain.