Fairly sure it is just short for application. They used to be called apps when we made them for J2ME phones. Symbian apps were not sandboxed, but J2ME ones we

Fairly sure it is just short for application. They used to be called apps when we made them for J2ME phones. Symbian apps were not sandboxed, but J2ME ones were, and this was the majority. Later on apple brought sandboxed apps to the iphone. And no-one knew what an app was back then, most seemed surprised that a person even made the games they played on their phones.