SNMP
A protocol network devices use to report their status and statistics to a monitoring system.
Switches, firewalls, printers, and UPS units all expose counters through SNMP: interface throughput, error rates, temperature, battery state. It is how a monitoring platform builds a picture of the network.
Versions 1 and 2c send a community string in clear text and should not be used across untrusted paths. Version 3 adds authentication and encryption.
Where this comes up
SNMP sits inside our networks and infrastructure work. If you are trying to work out what this means for your own environment rather than in the abstract, that is the page worth reading next, and a short call will get you a straight answer faster than either.