6590 Unassigned - User Port

6590 is a User Port. Transport Protocol , 6590 Service Name , Service Name Description: Unassigned.

Port	Protocol	Service Name	Description	Source
6590			Unassigned	IANA

Port	Service Name	Description
678	ggf-ncp	GNU Generation Foundation NCP
724		Unassigned
1207	metasage	MetaSage
1436	saism	Satellite-data Acquisition System 2
1734	cambertx-lm	Camber Corporation License Management
3088	xdtp	eXtensible Data Transfer Protocol
3251	sysscanner	Sys Scanner
3766		Unassigned
3790	quickbooksrds	QuickBooks RDS
4176	tl-ipcproxy	Translattice Cluster IPC Proxy

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