Android layout xml: difference between "app:" and "<ad_name>:"

Using any of these prefixes gives the same result:

    app:cardElevation="4dp"
    card_view:cardElevation="4dp"

      

        
        
        
      

    

Are these synonyms? And if so, why are both options?

EDIT

As the Doomsknight

comments say, this only happens when the namespace exactly matches (which makes sense).

However, I still don't understand where the difference between these prefixes lies.