PIM Dense Mode (PIM-DM) is a multicast routing protocol used in networks to efficiently distribute data to multiple receivers. It operates under the assumption that all nodes in a network want to receive the multicast traffic. PIM-DM uses a flooding mechanism to send data to all parts of the network, creating a shared tree for data distribution. When a receiver joins a multicast group, PIM-DM sends data to all routers in the network. If a router detects that no receivers are present, it prunes the multicast tree to stop unnecessary data transmission. This process helps optimize bandwidth usage while maintaining efficient data delivery.