A .pkg file is a package installer used on macOS. It's essentially an archive containing the files and instructions needed to install software, fonts, drivers, or other resources on a macOS system. These packages are often used to distribute applications, updates, and other software components. The .pkg file format is a standard way to bundle all the necessary files and scripts into a single, easily distributable file. When a user double-clicks a .pkg file, the macOS Installer application launches and guides the user through the installation process. This process typically involves accepting a license agreement, selecting an installation location, and entering an administrator password if required. The package can contain pre-installation and post-installation scripts that perform tasks such as checking system requirements, creating directories, setting permissions, and configuring the installed software. The .pkg format is a crucial part of the macOS software distribution ecosystem, ensuring a consistent and reliable installation experience for users.