Overlay networks are secondary networks built on top of existing blockchain infrastructure. They aim to enhance the functionality, scalability, or efficiency of the main network without altering its core structure.These networks facilitate specific tasks, such as reducing transaction fees or increasing transaction speeds. By allowing transactions and data to be processed off the main blockchain, overlay networks can help alleviate congestion and improve user experience.Examples of overlay networks include Layer 2 solutions like the Lightning Network for Bitcoin or zk-Rollups for Ethereum. These systems enable faster and cheaper transactions while maintaining the security and decentralization of the underlying blockchain.Overall, overlay networks serve as a means to expand the capabilities of blockchain technology, making it more practical for a broader range of applications.