A mobile application usually called a mobile app or simply an app is a computer program or software application designed to run on a mobile device such as a phone, tablet, or wearable devices like watches, glass, even on shoes. Apps were originally intended for productivity assistance such as email, calendar, and contact databases, but the public demand for apps caused rapid expansion into other areas such as mobile games, factory automation, GPS and location-based services, order-tracking, and ticket purchases so that there are now millions of apps available.

Apps are generally downloaded from application distribution platforms that are operated by the owner of the mobile operating system, such as the App Store (iOS) owned by Apple Inc. or Google Play Store owned by Google. Some apps are free, and others have a price, with the profit being split between the application's creator and the distribution platform. Mobile applications often stand in contrast to desktop applications which are designed to run on desktop computers, and web applications that run in mobile web browsers rather than directly on the mobile device.