"App" usually refers to a software application, or program, on a mobile platform. The term was in use before the popularization of smartphones and mobile platforms to refer to computer programs in general. Since Mac OS X, applications on the Macintosh computer use a ".app" file name extension. However, possibly due to Apple Inc.'s marketing, the term has become most closely associated with mobile platforms, including iOS and Android.
Mobile Apps tend to be more limited than traditional software because of company restrictions on what an app can do if they are offered on the company's app store, such as enforced sandboxing. Today most Apps are run on Restricted Platforms. They typically utilize telemetry which may identify and tracks users. However, FLOSS and ethically designed apps are also available which respect users' privacy (See FLOSS App Stores).