iOS app
From Just Solve the File Format Problem
An IOS app file (.app) is actually a subdirectory (folder), in the OS X bundle file fashion where it appears to be a single file when viewed within Apple systems. It contains all the files composing an app for use in the iOS system (on iPhones, iPads, etc.) including executables and support files such as graphics and sounds. It will normally be found packed into an IPA archive for installation, though the raw .app file/folder is present on developers' systems when the project is built in Xcode.
