A subsystem is a smaller, self-contained system that operates within a larger system. It has its own specific functions and components, but it also interacts with other subsystems to contribute to the overall performance of the larger system. For example, in a car, the engine is a subsystem that works with other subsystems like the transmission and braking system. Subsystems can be found in various fields, including engineering, biology, and computer science. In a computer, the operating system acts as a subsystem that manages hardware and software resources, while applications like word processors and spreadsheets serve as additional subsystems that perform specific tasks.