Unregistered and unnamed — a bare high port with no standard service behind it.
65310 falls in the Dynamic/Private range that RFC 6335 sets aside at 49152-65535, which IANA does not assign, so there is no registered service name for it. Nmap's service database lists it as unknown and records it open on about 0.015% of scanned hosts, putting it around 1,250th out of the 8,000-odd TCP ports Nmap tracks. In practice a 65310 you see is almost always an ephemeral client socket — Windows and macOS/BSD allocate outbound source ports from 49152-65535 — or a service someone deliberately parked on an arbitrary high port. Nothing well-documented, and no notable malware, claims it.
Expose with care
The port itself carries no verdict; whatever you find listening does. Identify the process before deciding, and do not treat the high number as protection — scanners sweep the full range.
$ sudo lsof -nP -iTCP:65310 -sTCP:LISTENSeen 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.