An App, derived from the long form of the term "application", is the general term used for all kinds of applications i.e. computer programs - here, it is specifically used for applications on smartphones or mobile phones. These programs are mostly purchased or downloaded from one of the online shops encorporated into the respective operation system of each smartphone or from other official download stores run by the provider of the smartphone. They are installed directly onto the smartphone. That's why you will also find DeepView at your Apple App Store or at the Android Market.