A Linux distribution, often simply distribution or distro, is a member of the Linux family of Unix-like computer operating systems. Such systems are built from the Linux kernel and assorted other packages, such as the X Window System and software from the GNU project. Distributions optimized for size tend to use more compact alternatives like busybox, uclibc or dietlibc. There are over three hundred Linux distributions, all of which are implementations of the Linux operating system. Because most (if not all) of the kernel and supporting packages are some combination of free software and open source, Linux distributions have taken a wide variety of forms — from fully featured desktop and server operating systems to minimal environments (typically for use in embedded systems, or for booting from a floppy disk). Aside from certain custom software (such as installers and configuration tools) a "distro" simply refers to a particular assortment of applications married with a particularly compiled kernel, such that its "out-of-the-box" capabilities meets most of the needs of its particular end-user base.

There are currently over three hundred Linux distribution projects in active development, constantly revising and improving their respective distributions. One can distinguish between commercially backed distributions, such as Fedora (Red Hat), SUSE Linux (Novell), Ubuntu (Canonical Ltd.), and Mandriva Linux and community distributions such as Debian and Gentoo. The procedures for assembling and testing a distribution prior to release tend to become more elaborate the larger the user base.