The Port

In the low level TCP or UDP communications, a Port number is used to select one or more services on a machine and to uniquely identify multiple requests from a client. Default ports are defined, such as 80 for HTTP and 433 for HTTPS and therefore do not typically need to be specified in the URL. By specifying a Port possibilities exist to use a different service to communicate, or address a different site. This is useful, but not the norm.