An Operating System is a program (a set of instructions) that gets loaded into a computer when it is first turned on.
It manages all of the other applications on the computer (like word processors, games, web browsers, etc.), and lets them (and the user) interact with each other and with the computer's hardware (the hard disks, keyboard, monitor, printer, etc.)
(MSDOS, Windows and MacOS are other examples of Operating Systems.)
Presented by the Linux Users' Group of Davis
to the California 4-H Leadership Conference
August 10th, 2002 - UC Davis, California