The plug is what is on the end of the cord.

What is on the wall is a receptacle.

So you are talking about a receptacle cover plate.

But the most generic term is switch plate because the companies make the same produces for both and some combination.

I am not sure, but I think that the Sierra is the same as the Depard

Even if not they can sometime stamp other configuration.

And they have several different metals and finishes.

http://www.switchhits.com/switchplates_c_light_switch_plates_covers_g.html

http://www.wallplatewarehouse.com/?gclid=CN6PnPS9kZUCFQqdnAodUj7fgw

http://www.switchplategallery.com/new_news.php

The Sierra's have a super clean look - just brushed metal with two horizontal lines, one top, one bottom.