5901 Unassigned - User Port

5901 is a User Port. Transport Protocol , 5901 Service Name , Service Name Description: Unassigned.

Port	Protocol	Service Name	Description	Source
5901			Unassigned	IANA
5901	TCP		VNC	bekkoame

Port	Service Name	Description
2884	flashmsg	Flash Msg
3342	webtie	WebTIE
6499		Unassigned
6673	vision-elmd	vision_elmd IANA assigned this well-formed service name as a replacement for "vision_elmd".
8237		Unassigned
9017		Unassigned
9052		Unassigned
9075		Unassigned
9396	fjinvmgr	fjinvmgr
9872		Unassigned

A port is an endpoint of communication in an operating system. While the term is also used for hardware devices, in software it is a logical construct that identifies a specific process or a type of service.

Port numbers are assigned in various ways, based on three ranges: System Ports (0-1023), User Ports (1024-49151), and the Dynamic and/or Private Ports (49152-65535);

The Well Known Ports are assigned by the IANA and on most systems can only be used by system (or root) processes or by programs executed by privileged users. Ports are used in the TCP [RFC793] to name the ends of logical connections which carry long term conversations. For the purpose of providing services to unknown callers, a service contact port is defined. This list specifies the port used by the server process as its contact port. The contact port is sometimes called the "well-known port". To the extent possible, these same port assignments are used with the UDP [RFC768]. The range for well-known ports managed by the IANA is 0-1023.
DYNAMIC AND/OR PRIVATE PORTS Registered Ports are those from 1024 through 49151.
The Dynamic and/or Private Ports are those from 49152 through 65535