An abbreviation for "application". The filename extension .app means application in Symbian OS, SkyOS, GNUstep and Mac OS X. On the latter two systems, a .app file is actually a folder containing binaries and supporting files. On Windows, AppWave from Embarcadero supplies the support to run .app Windows binaries. An "App" may also refer to a lightweight application, tailored to a device's form factor and input-output interfaces (key pad, touch pad, remote control, display, etc). Devices may include such things as a mobile phone, a TV set, a cable or satellite receiver, a tablet PC, a printer - any device whose features can be extended through software. Source: