In communication networking, a networking port (usually shorted to just plain 'port') mostly refers to a particular communication channel at a given host. This allows different applications, running at the same time (usually in separate processes) to each receive data destined to them when traffic arrives from the network.
In the TCP/IP protocol suite, both TCP and UDP have ports; each packet in both protocols has a pair of port numbers in it (one for the port on the source host, and one for the destination).
The term may also refer to the place (and connector) where a host is connected to a physical network; e.g. an Ethernet connector. IMPs also have ports on them, where the hosts plug into them.