The Full Form of OBB is‍ Opaque binary blob.

Opaque binary blob is a term used in network engineering and computer science to refer to a sizeable piece of data, which looks like binary garbage from outside, by entities which do not know what that blob denotes or carries, but make sense to entities which have access permission and access functions to them.

OBB lets you package up large files and store them on the public SDcard in a way that only your app can decrypt and use them. After building the AOSP the mkobb.sh and obbtool allow you to create (on Linux) OBB files.

The OBB file format was developed by Google for its Android system. This file format is used by Android app developers to package large files that are used by their apps on the user’s Android device.

There are shared and proprietary .obb files. Resources stored in shared OBB files can be used by different apps. For example, an OBB file with map data may be shared and used by Android apps that have been granted access rights to the map data in those .obb files.

Proprietary OBB files, on the other hand, are unique to a single app.

Android developers use Linux applications like Obbtool and MKOBB.SH to create .obb files. It’s recommended to leave these OBB files alone, in order to ensure that the Android apps that need to use them can continue to work properly.