Not too happy with you using autism to call someone dumb, but I'll leave this up assuming it was just a one-off.
Definition of sash for Students. 1  1 : a frame for a pane of glass in a door or window. 2  2 : the movable part of a window.
A sash window. A sash window or hung sash window is made of one or more movable panels, or sashes, that form a frame to hold panes of glass, which are often separated from other panes (or lights) by glazing bars, also known as muntins in the US (moulded strips of wood).