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.
Sash curtains are used to cover the lower sash of the windows. Rod pocket curtains have a channel sewn into the top of the fabric. A curtain rod is passed through the channel to hang. Thermal or Blackout curtains use very tightly woven fabric, usually in multiple layers. They not only block out the light, but can also serve as an acoustic or thermal dampener.