By 'Bundle' I believe that he simply means the way an "App" is packaged...

All those neat little App-like files that you just drag and drop into your Applications folder are really just fancy folders that contain files, yet act like an executable file. If you hold down the Option button while you right click on an "App" you'll see the option "Show Package Contents" to see the contents. If you select this you can go in and modify the contents. If your case add textures, audio files, etc...