A Linux distribution (also known as a "distro") is an open-source operating system based on the Linux kernel. Besides the kernel, the usual components of a desktop Linux distribution are GNU tools and libraries, a package manager, a windowing system (like X11 and Wayland), a window manager (such as KWin and Compiz), and a desktop environment (like GNOME and KDE). Linux server distributions typically do not feature the GUI components.
Popular Linux distributions include Ubuntu, Fedora, CentOS, Linux Mint, Arch Linux, Red Hat, and others. While most are available free of charge, some, like Red Hat Enterprise Linux, offer subscriptions for service and support.