A casement is a window that is attached to its frame by one or more hinges.Casement windows are hinged at the side. (Windows hinged at the top are referred to as awning windows.Ones hinged at the bottom are called hoppers.) They are used singly or in pairs within a common frame, in which case they are hinged on the outside. Casement windows are often held open using a casement stay. casement is a window that is attached to its frame by one or more hinges.