591 FileMaker, Inc. - HTTP Alternate (see Port 80) - System Port

591 is a System Port. Transport Protocol TCP UDP , 591 Service Name http-alt, Service Name Description: FileMaker, Inc. - HTTP Alternate (see Port 80).

Port	Protocol	Service Name	Description	Source
591	TCP UDP	http-alt	FileMaker, Inc. - HTTP Alternate (see Port 80)	IANA
591	TCP		FileMaker 6.0 (and later) Web Sharing (HTTP Alternate, also see port 80),Official	wikipedia
591	TCP UDP	http-alt	FileMaker, Inc. - HTTP Alternate (see Port 80)	bekkoame

Port	Service Name	Description
2273	mysql-im	MySQL Instance Manager
2802	veritas-tcp1	Veritas TCP1
3485	celatalk	CelaTalk
4844	gw-log	nCode ICE-flow Library LogServer
5359	ms-alerter	Microsoft Alerter
6306	ufmp	Unified Fabric Management Protocol
6480	sun-sr-http	Service Registry Default HTTP Domain
6653	openflow	OpenFlow
7633	pmdfmgt	PMDF Management
8359		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