A network sniffer is just as it sounds; a software tool that monitors, or sniffs out the data flowing over computer network links in real time. It can be a self-contained software program or a hardware device with the appropriate software or firmware.
Network sniffers can take snapshot copies of the data without redirecting or altering it. Some sniffers work only with TCP/IP packets, but the more sophisticated tools can work with many other network protocols and at lower levels, including Ethernet frames.
Years ago, sniffers were tools used exclusively by professional network engineers. Nowadays, however, with software applications available for free on the web, they are also popular with internet hackers and people just curious about networking.
Note: Network sniffers are sometimes referred to as network probes, wireless sniffers, Ethernet sniffers, packet sniffers, packet analyzers, or simply snoops.
https://www.lifewire.com/definition-of-sniffer-817996
A sniffer can be a piece of software or a human administrator who checks for access or the presence of intruders.
I lifted this from a book called Intelligence Collection by Robert M. Clark.
So Q has his lingo down pat.