/system
is read-only without root so it prevents uninstalling applications from /system/app
and /system/priv-app
. Applications that are critical are put there so that they can't be uninstalled. Carrier bloatware that they don't want to let you remove is also put there. The latter category of apps can be removed if you are rooted; the former, not so much./system/priv-app
also allows apps installed there to use signatureOrSystem
and other privileged permissions. Stephen's answer has some examples.user
apps from internal memory to the sd card. System apps cannot be moved and always take up some internal space. Most (all?) devices, though, have internal user apps on a different partition, so uninstalling a system app would not give you any more user app space (other than the dalvik-cache being removed).