What in the world is a window sash?
A window sash is the part of a window that moves and holds the glass panes together. The sash fits inside the window frame, which is attached to the house.
The sash will vary slightly depending on the type of window. For example, on a double hung window there is an upper and lower sash that move up and down. Having two sash makes the double hung window the easiest window style to operate and clean. Both sash also tilt in so that you can clean the outside of the window from inside your home.
A slider window only has one sash and, unlike on a double hung, the sash on a slider window glides left to right.
Casement windows also have only one sash. However, a casement window sash operates with a crank handle as opposed to sliding in the window frame.
*This article was reprinted from https://www.simonton.com/blog/window-sash/