Unregistered and rarely seen — identify the listener, the number tells you nothing.
There is no IANA registration for 9198 and nmap's table records it as unknown with a very low hit rate. It is close enough to PaperCut's 9191/9192 pair that an office host may have a related private listener, but that is a guess, not a fact. A version scan or a look at the host's own listening sockets is the only honest answer.
Expose with care
No default service means no default verdict; classify it once you know what answers there.
$ nmap -sV -Pn -p 9198 TARGETSeen this on your network? Beige Box scans your Wi-Fi and shows every open port on every device — and its Ports tool links straight back here.
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Corrections or a missing port? Reply @rimrocksystems.