Unregistered and uncommon; nothing standard claims 9290.
The IANA registry has no assignment for 9290 and nmap lists it as unknown. Like the rest of the sparsely used 9200-9400 range it shows up as an application's arbitrary choice rather than as a protocol. Fingerprint the listener rather than reading meaning into the number.
Expose with care
The verdict belongs to whatever service is bound there; establish that first.
$ nmap -sV -Pn -p 9290 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.