Pronounced lee-nucks. Linux is a computer operating system and its kernel. It is one of the most prominent examples of free software and of open-source development: unlike proprietary operating systems such as Windows and Mac OS, all of its underlying source code is available to the public and anyone can freely use, modify, and redistribute it.

In the narrowest sense, the term Linux refers to the Linux kernel, but it is commonly used to describe entire Unix-like operating systems (also known as GNU/Linux) that are based on the Linux kernel combined with libraries and tools from the GNU project and other sources. Most broadly, a Linux distribution bundles large quantities of application software with the core system, and provides more user-friendly installation and upgrades.

Initially, Linux was primarily developed and used by individual enthusiasts. Since then, Linux has gained the support of major corporations such as IBM, Hewlett-Packard, and Novell for use in servers and is gaining popularity in the desktop market. Proponents and analysts attribute this success to its vendor independence, low cost, security, and reliability.

Linux was originally developed for Intel 386 microprocessors and now supports all popular computer architectures (and several obscure ones). It is deployed in applications ranging from embedded systems (such as mobile phones and personal video recorders) to personal computers to supercomputers.