Window class (application) versus whole window class for KWin rules?


An application can have many windows and each instance of application window can have special name (that can differ from other instance names). So when a rule only checks application class, it applies to all window instances of the application. If you select Whole Window Class then you can target a specific window class instance of application.

If you are interested into background details, this comes from InterClient Communication Conventions Manual (ICCCM) - WM_CLASS Property.