Simple answer: com1 would refer to "communications port 1". The four "classic" com ports are com1-com4, although more recent versions of Windows support higher numbered ports. Medium answer: A com port is also known as a serial port. These are represented physically by connections on the back (usually) of your computer. Your mouse and keyboard probably plug into com ports (unless they're USB devices). Sometimes cards (especially modems) inside your computer will be a com port - but the devise itself uses its own com port, and so you don't plug anything into the card's com port (although you might plug, for instance, a phone line into a modem, which would have a com port on the modem card itself). (If you're saying "Cards? What?" Most of the things you plug things into in the back of the computer are the only visible edge of a card, but that's really getting way beyond the scope of this answer) Some more possible ports you might see: lpt1 - "Line PrinTer" port #1, with other numbers possible. con - "CONsole" port, which would be a monitor There are several more, but those are the easier to discuss... These ports are used by programs and operating systems to communicate with specific hardware devices. For instance, a program might want to print out a statement. It might direct the statement to "con" (most often not using that term, but that's outside the scope of this answer), and the statement might appear on the screen. Or, it might direct the statement to "lpt1", and that might then print on a printer. Or, a computer might need to send communications to a modem, which might be attached to com3, so the computer would send and receive to com3. If your mouse was plugged into com2, that's the port your computer would receive inputs from your mouse on -- and if your computer tried to communicate with the modem on com2, it wouldn't work. In a practical sense, these terms have become somewhat outdated for the most part, for the non-technical computer user. In the old days, you might have to know what port something was using, along with a number of other inconvenient settings, to get things to work. But now, you can often plug a USB device in, and nobody cares what port is being used - USB handles it for you automatically. I've tried to cover several possible directions your question might take, and none of this is very technical in depth.

It stands for communications port, and in the case of COM ports, it almost always refers to what is called a "serial" port. This refers to a method of transfering bytes of data once bit at a time, one after the other. This is done by sending electric pulses in either a positive or negative voltage to represent 0 or 1 (binary). There is another common name for this transfer method that you may have heard passed around, RS232 (this is the name of the protocol, or world wide standard for transmitting data in this method). As far as the physical connections, the most common used has 9 pins (those holes or gold pin looking things on the cable), but only three of the pins are commonly used. One is used to transmit, one is used to recieve, and one is used to ground the connection to prevent stray voltage from making the bits (positive or negative voltage) from being unusable.