DSR, or Dynamic Source Routing, is a protocol used in mobile ad hoc networks. It allows devices to communicate with each other without a fixed infrastructure by dynamically discovering routes as needed. This is particularly useful in situations where traditional networking methods are impractical, such as in disaster recovery or military operations. In DSR, each device maintains a route cache that stores the paths it has learned. When a device wants to send data, it checks its cache for a valid route. If none exists, it initiates a route discovery process, broadcasting a request to find a suitable path to the destination.