1 TCP Port Service Multiplexer - System Port

1 is a System Port. Transport Protocol TCP UDP , 1 Service Name tcpmux, Service Name Description: TCP Port Service Multiplexer.

Port	Protocol	Service Name	Description	Source
1	TCP UDP	tcpmux	TCP Port Service Multiplexer	IANA
1	TCP UDP		TCP Port Service Multiplexer (TCPMUX),Official	wikipedia
1	UDP		Sockets des Troie	anti-trojan
1	UDP		(UDP) - Sockets des Troie	simovits.com
1	TCP UDP	tcpmux	TCP Port Service Multiplexer	bekkoame
1	UDP		Sockets des Troie	bekkoame

Port	Service Name	Description
500	isakmp	isakmp
559	teedtap	TEEDTAP
1928	emsd-port	Expnd Maui Srvr Dscovr
2668	alarm-clock-c	Alarm Clock Client
2745	urbisnet	URBISNET
4729		Reserved
5343	kfserver	Sculptor Database Server
5754		Unassigned
6559		Unassigned
6706		Reserved

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