What is a Port in networking?

Port is simply a channel of communication which is numbered between 1 and 65536.It is a kind of subaddress. The IP address is the primary address and the port is the subaddress. Each port is associated with a specific process or service. For example:Port 80 is assosciated for HTTP messages.

Making thing simpler, just think of the IP address as the street address of a building and then the port as the apartment number. I need the street address to get to the right building, but I need the apartment address to find who I am looking for. This is the same with ports. The IP address gets us to right machine, but the port takes us to correct service, say HTTP on port 80.

There are 65,536 ports. The first 1,024 are generally referred to as the common ports.
Some of the ports are:

Port Number	Usuage
80	Hypertext Transfer Protocol (HTTP)
443	HTTP Secure (HTTPS) HTTP over TLS/SSL
20	File Transfer Protocol (FTP) Data Transfer
21	File Transfer Protocol (FTP) Command Control
22	Secure Shell (SSH)
23	Telnet - Remote login service, unencrypted text messages
25	Simple Mail Transfer Protocol (SMTP) E-mail Routing
53	Domain Name System (DNS) service
119	Network News Transfer Protocol (NNTP)
123	Network Time Protocol (NTP)
143	Internet Message Access Protocol (IMAP) Management of Digital Mail
161	Simple Network Management Protocol (SNMP)
194	Internet Relay Chat (IRC)