Game control adapter
Originally known as the Analog-to-Digital port (A-to-D port), the as a game port, joystick port, or game control adapter is a 15-pin connector port first found on IBM computers in 1981. The game port is handled by the SIO and allows users to connect such devices as joysticks, game pads, steering wheels and other devices that allow additional functionality to the computer.
In the picture is an example of the back of a computer sound card. In this picture, the joystick port is the 15-pin yellow connection at the bottom of the card.
Today, this port has been largely replaced by game devices that connect using USB and the 15-pin connector is no longer used.