The TCP/IP protocol is designed such that each computer or device in a network has a unique "IP Address" (Internet Protocol Address) and each IP address can open and communicate over up to 65535 different “ports” for sending and receiving data to or from any other network device.
The TCP address uniquely identifies the computer or device on the network and a "Port Number" identifies a specific connection between one computer or device and another (i.e between two IP Addresses). A TCP/IP "port" can be thought of as a private two-way communications line where the port number is used to identify a unique connection between two devices.
The concept is very similar to any other type of port on your PC (serial, parallel, etc) except that instead of having a physical connection, the TCP/IP protocol creates a "virtual IP port" and the network hardware and software is responsible for routing data in and out of each virtual IP port.
