An OBB file is an expansion file used by the Android operating system to store additional data for applications. Because Android application packages (APKs) are limited in size, developers often use OBB files to store large assets such as high-resolution graphics, media files, and other large data that are essential for the application to function correctly. These files are typically downloaded separately from the main APK and stored on the device's external storage or in a designated location within the internal storage. OBB files are usually encrypted or obfuscated to protect the application's assets from unauthorized access or modification. They are often used for games with extensive textures and audio, or applications with large amounts of pre-rendered content. The Android system provides APIs for accessing and managing OBB files, allowing applications to seamlessly integrate the data stored within them. The OBB file format itself is essentially a ZIP archive, often containing multiple files and directories organized in a specific structure that the application expects. When the application needs to access the data, it uses the Android APIs to mount the OBB file and access its contents as if they were part of the application's file system.