Cladding is the application of one material over another to provide a skin or layer intended to control the infiltration of weather elements, or for aesthetic purposes.
Cladding does not necessarily have to provide a water-proof condition but is instead a control element. This control element may only serve to safely direct water or wind in order to control run-off and prevent infiltration into the building structure. Cladding applied to windows is often referred to as window capping

Window capping

In building construction, window capping refers to the application of one material over another to provide a weather-proof layer, intended to control the infiltration of weather elements....

and is a very specialized field.