Final answer:
In TCP/IP communications, a program on one system exchanges information with the same program on a remote system, which is facilitated through the use of a port.
Step-by-step explanation:
When using TCP/IP, most communication involves exchanging information between a program running on one system and the same program running on a remote system. TCP/IP uses a 16-bit numeric value called a port to identify the resources to be used for the exchange. Therefore, the completed statement is: 'When using TCP/IP most communication involves exchanging information between a program running on one system and the same program running on a remote system. TCP/IP uses a 16-bit numeric value called a port to identify the resources to be used for the exchange.'