A program installed as memory resident, and launched during start-up or coincident with another application, so as to be immediately available whenever a "hot key" keyboard combination is executed. When activated, the pop-up utility overlays any other application until closed for later recall. It differs from task-switching in that the primary program remains displayed, and the pop-up utility often interacts with that program, such as in a dictionary or search procedure. In MS-DOS systems, this utility is known as a "terminate and stay resident" (TSR) program.