Difference between 'Administrator' and root privileges There is an app called smart app lock. It has an option to prevent uninstalling of the app. Ticking it gives confirmation to add app to system administrators. 

Root was not required to make it work. What privileges does this 'Administrator' get? I know that root has more privileges as I could uninstall it with root privileges, but what is the difference between the privileges of admin and those of root?
Device Administrators are apps which the user grants certain privileges. For example:


Password policies (minimum length, expiration time, etc.)
Lock screen (say, after a given time)
Require storage encryption
Remotely wipe the device
Disable camera


And some other options, including the possibility to prevent uninstalling of the app. 

So the difference is that with root you gain the possibility to modify the system at all levels, instead with administrator you can gain control over a limited set of options - which are of course available to root. 

Another difference is that administrator permissions are built-in in stock Android and available to apps developer through the dedicated API.
You can see which permissions are granted to which apps and revoke them by going to Settings -> Security -> Device administrators.