plate glass

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A strong rolled and polished glass containing few impurities, used for mirrors and large windows.

from The Century Dictionary.

• noun A superior kind of thick glass used for mirrors, and also for large panes in windows, shop-fronts, etc. (See Plate, 12.)

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun sheet glass; a type of glass, initially produced in plane form, commonly used for windows, windshields, etc.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun glass formed into large thin sheets