An interface on a computer to which you can connect a device. Personal Computers have various types of ports. Internally there are several ports for connecting disk drives, display screens, and keyboards. Externally, personal computers have ports for connecting modems, printers, mice and other peripheral devices.
Serial ports used to connect modems, serial printers and other peripherals to your computer. Each port is assigned its own individual number, IO address, and Interrupt Request Line. COM1 and COM2 are usually the physical serial ports you can see on the back of your computer (9-pin and 25-pin DB connectors). COM3 and COM4 are usually virtual communications ports for internal devices connected via the expansion slots inside your computer.
A connector for a communications interface, usually, a serial port.