well-known port

A number from 0 through 1023 used to identify a network service on an IP network (the Internet). Residing in a field in the TCP or UDP header, the port number directs packets to the appropriate application in the server. The most well-known port is 80, which identifies HTTP traffic for a Web server.

Registered and Private Ports
The Internet Assigned Numbers Authority (IANA) registers ports 1024 to 49151 for the convenience of the Internet community. Port numbers from 49152 to 65535 are private ports, also called "dynamic ports." For the complete list of well-known ports and registered ports, visit www.iana.org/assignments/port-numbers. See port number, port scanning, ICANN and IANA.

 COMMON WELL-KNOWN PORTS

 Service   Port      Function

 HTTP      80        Web
 HTTPS     443       Web (secure)
 FTP       20,21     File transfer
 FTPS      989,990   File transfer (secure)
 Telnet    23        Remote login
 SSH       22        Remote login (secure)
 DNS       53        Host naming

 SMTP      25        Internet mail
 POP3      110       Client access
 IMAP      143       Client access

 NNTP      119       Usenet newsgroups
 NNTPS     563       Usenet newsgroups (secure)
 IRC       194       Chat

 NTP       123       Network time

 SNMP      161,162   Network management
 CMIP      163,164   Network management

 Syslog    514       Event logging
 Kerberos  88        Authentication
 NetBIOS   137-139   DOS/Windows naming

(networking)

well-known port - A TCP or UDP port with a number in the range 0-1023 (originally 0-255). The well-known port numbers 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.