What does "App" mean?

App:

An Application [App] is a program one downloads and runs on a mobile device or a computer. The Facebook App, running on your smart phone, is one example of one app. Apps are typically downloaded from an app store such as Apple's App Store, Google's Play Store, Samsung's Galaxy Apps, or Amazon's Appstore. Apps can connect seamlessly with a website. Example: The Accuweather app connects with the Accuweather.com website to show your local weather on your phone or tablet.

 BuildFire: App Stores List