A terminate and stay resident (TSR) program is one that is set up to be loaded and then remain in computer memory so that it is quickly accessible when a user presses a certain keyboard combination. TSR programs are used in Disk Operating Systems and perhaps other non-task operating systems. They aren't needed in multitasking systems such as Windows and OS/2. TSR programs typically include calculators, clocks, and notepads. When running another program in DOS, you can press the preset keyboard key or combination of keys and the TSR program will "pop up" into view.