An Android app is a software application running on the Android platform. Because the Android platform is built for mobile devices, a typical Android app is designed for a Smartphone or a tablet PC running on the Android OS.
It has a user interface based on direct management. Android has created mainly for touch screen mobile devices such as computers, with dedicated user interfaces for televisions (Android TV), for cars (Android Auto), and for wrist watches (Android Wear).
The OS uses touch inputs that generally match to real world actions like swiping, tapping, pinching, and reverse pinching to influence on-screen objects, and a virtual keyboard.