operating system n.
[techspeak] (Often abbreviated `OS') The foundation software
of a machine; that which schedules tasks, allocates storage, and
presents a default interface to the user between applications.
The facilities an operating system provides and its general
design philosophy exert an extremely strong influence on
programming style and on the technical cultures that grow up
around its host machines. Hacker folklore has been shaped
primarily by the Unix, ITS, TOPS-10, TOPS-20/TWENEX, WAITS,
CP/M, MS-DOS, and Multics operating systems (most importantly by
ITS and Unix).