They are the special format files that developers get when the APK file of application is extracted.

They are the format of files provided by Play Store against any paid application that can be used to extract the APK file.

They are the additional file hosted by Google Play to overcome the size limit of your application’s APK file.

It is the additional file directly sent by the developer to the user (if requested) to overcome the size limit of your application’s APK file.