An abbreviation for Apple Desktop Bus. The bus used for connecting peripheral data entry devices to Macintosh computers. This is how things like the keyboard, mouse, track ball, joystick, and some tablets connect to a Macintosh. Since a bus architecture is used they can usually be connected through each other so that only one actually has to plug into the computer itself. The connector looks like a very small MIDI connector with only four pins. In fact, it looks exactly like an S-Video connector (in a pinch an ADB cable can be used for S-Video and vice versa). The Apple Desktop Bus has been part of every Macintosh computer to date but may begin to be phased out in favor of the faster and more robust USB (Universal Serial Bus).