Android app is a software application running on the Android platform because the Android platform is built for mobile devices and is designed for Smartphone, tablet and PC which is running on the Android OS.
Although an Android app can be made available by developers through their websites, most Android apps are uploaded and published on the Android Market, an online store dedicated to these applications. The Android Market features both free and priced apps.
Android apps are written in the Java programming language and use Java core libraries. They are first compiled to Dalvik executables to run on the Dalvik virtual machine, which is a virtual machine specially designed for mobile devices.