The term I/O means “input” and “output”. An I/O card facilitates communication with the computer by sending and receiving data. I/O is one of the three main components of computers. Basically, for every input, there’s an output. You pull up a document on your computer and use the keyboard to print it. The keyboard is the input and the printer is the output. This is a simple explanation of I/O, but it’s a good start to help explain what I/O cards are and how they work.