Linux refers to the family of Unix-like computer operating systems using the Linux kernel. If your question is about a certain distribution only, use a more specific tag.
The name "Linux" originates from the Linux kernel, originally written in 1991 by Linus Torvalds. The main supporting system tools and libraries from the GNU Project (announced in 1983 by Richard Stallman) are the basis for the Free Software Foundation's preferred name GNU/Linux.
Linux is used on a broad range of computer hardware, including: microcomputers, mainframes, mobile phones, supercomputers, tablet computers, game consoles, set top boxes, and routers. Linux is packaged as a distribution which typically includes the kernel itself and all the various utilities, libraries and applications intended for that particular distribution. It is of note that in most cases, the underlying source code is both free and open source.
Most Linux questions on Super User are about …