Linux
also: GNU/Linux, kernel
Linux is a free and open-source operating system kernel created by Linus Torvalds in 1991 that manages hardware resources and enables software to run on computers. It forms the core of Linux distributions like Ubuntu, Fedora, and Debian.
Linux is the kernel—the central software component that directly controls your computer's hardware. It handles memory management, process scheduling, device drivers, and file systems. When you run a Linux machine, the kernel is constantly working behind the scenes to allocate CPU time, manage RAM, and coordinate communication between programs and hardware.
A Linux distribution (or distro) is Linux bundled with additional software like package managers, shells, and utilities. For example, Ubuntu packages the Linux kernel with GNOME desktop and APT package manager, while servers might use CentOS or Debian with minimal graphical tools.
Linux powers everything from smartphones (Android uses a Linux kernel) and personal computers to web servers and supercomputers. Because it's open-source, anyone can view, modify, and redistribute the code under licenses like the GPL.