Pacman is a software package manager, developed as part of the Arch Linux distribution. It was created by Arch Linux creator Judd Vinet. The Pacman package manager is one of the major pillars of Arch Linux.
Pacman is capable of resolving dependencies and automatically downloading and installing all necessary packages. In theory, a user need only run a single command to completely update the system. In addition to Arch Linux, Pacman is also used by many other distributions.
Pacman combines a simple binary package format with an easy-to-use build system (see makepkg and ABS). This makes it possible to easily manage packages, whether they be from the official Arch repositories or the user's own builds.
Pacman keeps the system up to date by synchronizing package lists with the master server. This server/client model also allows users to download/install packages with a simple command, complete with all required dependencies. Pacman uses compressed tar archives for all of the packages, each of which contains compiled binaries. Packages are downloaded via FTP; it can also use HTTP and local files, depending on how each repository is set up. It complements the Arch Linux Build System (ABS) used to create packages from source.