273 Unassigned - System Port

273 is a System Port. Transport Protocol , 273 Service Name , Service Name Description: Unassigned.

Port	Protocol	Service Name	Description	Source
273			Unassigned	IANA

Port	Service Name	Description
1171	atc-appserver	AT+C FmiApplicationServer
1305	pe-mike	pe-mike
1925	discovery-port	Surrogate Discovery Port
2221	rockwell-csp1	Rockwell CSP1
2614	neveroffline	Never Offline
2820	univision	UniVision
3213	neon24x7	NEON 24X7 Mission Control
4180	httpx	HTTPX
4262	vrml-multi-use	VRML Multi User Systems
4516		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