pkg (package) is a filename extension used for several file formats that contain packages of software and other files to be installed onto a certain device, operating system, or filesystem, such as the macOS, iOS, PlayStation Vita, PlayStation 3, and PlayStation 4. It contains installation information in plain text that defines how to build the SIS installer file. Oftentimes PKG files will also be used to update NeXT installer packages. pkg is an OS X Installer file. A PKG file, diminutive of "Package", is simply a package of installation files. A PKG file is a database file created by programmers for Symbian OS devices containing information in text format used to create a SIS file.