Broadcast, unknown-unicast and multicast traffic
Broadcast, unknown-unicast and multicast traffic (BUM traffic) is network traffic transmitted using one of three methods of sending data link layer network traffic to a destination of which the sender does not know the network address. This is achieved by sending the network traffic to multiple destinations on an Ethernet network.
Source: Wikipedia — Broadcast, unknown-unicast and multicast traffic (CC BY-SA 4.0)