What is Linux?

Linux is an operating system that evolved from a kernel created by Linus Torvalds when he was a student at the University of Helsinki.

To say that Linux is an operating system means that it's meant to be used as an alternative to other operating systems, Windows, Mac OS, MS-DOS, Solaris and others.

 Linux is not a program like a word processor and is not a set of programs like an office suite. Linux is an interface between computer/server hardware, and the programs which run on it.