Stile
This piece of a window frame runs up and down on both sides
On a window sash's frame, the stiles are the vertical pieces on the left and right of the window pane. Like rails, they have grooves for placing the panes in. Cross muntins extend horizontally from stile to stile.
Like rails, stiles are also used to label parts in furniture. They reference vertical components.
Cross muntins run from stile to stile.
Stiles are usually much wider than muntins and can be narrower than rails.