APP, Mac OS X Application (.app)
The APP Executables file format
APP is the file extension for executable files or application programs of the Mac OS X machine. They are comparable to Windows' EXE files. A double click runs the program associated with the APP file. With a right-click, the content of the APP file can be revealed to Mac OS X users. This is possible since APP files belong to the Mac OS package files.
Technical details of APP files
Typically, APP files contain executables and resources of the application associated with the file. Furthermore, icons, plugins and other files can be contained in the package. Moving or even editing files inside the APP package file is not advised. Any meddling with the contained files can result in the program of the APP file not being able to be executed properly or at all. Similar to EXE files, APP files can easily be infected with viruses or other malware. Make sure to thoroughly check and scan any unknown APP files.