SNMP traps
An SNMP trap is a message that is initiated by a network element and sent to the network management system. Often, traps indicate a failure of some sort, such as a router message indicating a power supply failure, or a printer message indicating an "out-of-ink" condition.
If an SNMP trap enters the system, and Resource Manager cannot identify the event (the event is classified as "/Unknown"), then you can classify the event so that the system handles it consistently.