A DMG file is an Apple Disk Image file, a common format used on macOS to distribute software. It's essentially a digital container that holds compressed software installers, applications, or other files. Think of it as a virtual disk drive. When you open a DMG file, macOS mounts it as a volume on your desktop, allowing you to access its contents. This makes it easy to install applications or copy files to your computer. DMGs often include compression to reduce the file size for easier downloading and distribution. They can also be password-protected for security. The format supports various features like checksums to ensure data integrity and resource forks, which are specific to macOS. Once you've finished using the contents of a DMG file, you can unmount it, which removes the virtual disk from your desktop. DMGs are a standard way to distribute software and data on macOS, providing a convenient and secure method for packaging and delivering files.