File used by some Android apps sold on the Google Play online store; contains additional app data that is not stored in the main application package (.APK file), such as graphics, media files, or other large program assets; uses an encrypted format.

Since Google Play only allows APK files to be 50MB or smaller in file size, app developers must use different files to store additional app assets. Developers can use any format they choose, such as .ZIP or .MP4, but they can also use the JOBB tool provided with the Android SDK to bundle and encrypt assets together in an OBB file. These additional assets can be uploaded with the APK file using the Google Play Developer Console, and users that download the app will receive both the APK file and the additional asset files. NOTE: Any additional asset provided beyond the APK file is called an APK Expansion File.