The term "app" is an abbreviation for "application". An application is a software program designed to perform a specific function directly for the user or, in some cases, for another application program. Different types of apps include web apps, native apps, hybrid apps, killer apps, and legacy apps. The term "app" is commonly used in the context of mobile devices such as smartphones and tablets, where users can download and install apps from app stores such as the iTunes store for iPhones and the Google Play store for Android phones.