Final answer:
An iOS app is distributed as an IPA file, which is the format used for iOS App Store Packages. APP, EXE, and DMG files are associated with macOS and Windows and do not apply to iOS apps.
Step-by-step explanation:
An iOS app is distributed as a IPA file, which stands for iOS App Store Package. This type of file contains all of the necessary data to run the app on an iOS device. When you download an app from the App Store, your device is actually downloading an IPA file, which it then installs. Other file types like APP, EXE, and DMG serve different purposes: APP is a macOS application bundle, EXE is an executable file for Windows, and DMG is a disk image used on macOS.