View source for Afs:system-app

=== /system/app ===

A System application is NOT an application which is signed by the OS’s platform signatures.  A System application is merely an application which is placed under /system/app folder in an Android device. An application can only be installed in that folder if we have access to the OS’s ROM (system.img). The application is placed under /app folder after the ROM has been extracted. A device which loads the custom ROM will have the new System application added. The benefit of a System application is that the application cannot be removed from the device (cannot be uninstalled by the user). This is only because /system/app is a read-only folder.

* User installed apps apk's are stored at /data/app
* System apk's are stored at /system/app

You can push an .apk to the phone to the System partition to the folder "/system/app" using special software.  There are apps in Google Play that claim to do this.  Root is required.