The .PKG file extension refers to Mac OS x installer package file. This is a special type of archive file that can contain data and instructions for installing an application software on an Apple computer that runs Mac OS.

The .PKG files can be stand-along archive packages or they can be part of a bigger archive and are run in batch for installation using scripts. Usually the PKG package files are handled by the Installer application on the MAC OS computers. You can also see the contents of a package by right clicking it.