This document discusses mobile application development. It begins by defining a mobile app as a software application developed for smartphones and tablets rather than desktop computers. It then provides some key statistics about mobile phone and smartphone usage globally. It discusses the major mobile platforms of Android, iOS, Windows Phone, and BlackBerry and their programming languages. It also outlines the different types of mobile apps that can be developed - native apps, web apps, and hybrid apps - and describes their characteristics. The document is authored by Mosiur Rahman from the State University of Bangladesh and it provides contact information at the end.