TSR (terminate-and-stay-resident program)

A computer program, also known as a memory-resident program, that remains in memory after being run so that it can be called up later. These extend the capabilities of the operating system or provide "pop-up" functions (such as a calendar or calculator) that can be brought up in the middle of another program without disturbing that program. These programs were popular in the days of MS-DOS, but lead to numerous problems due to memory usage conflicts.