Linux refers to one or both of two things.
The heart of a Linux system is the Linux kernel, originally written by Linus Torvalds from Minix by Andrew Tanenbaum, and now maintained by hundreds of developers. It is a clone of Unix for personal computers and forms the heart of a system that is, to a reasonable extent, POSIX compliant.
Linux also refers to the name of the complete operating system built upon the Linux kernel, and there are literally hundreds (possibly thousands) of Linux operating system distributions, each one tailored to a specific need or set of needs.
Cards tagged Linux: