Rail and Stile

In any frame construction -- a face frame, a frame-and-panel door, a table apron assembly -- stiles are the vertical frame members, running the full height of the frame, while rails are the horizontal members that join between them. The vocabulary matters because it's how joinery and cutting lists get communicated precisely: "cut the rails to length" means something specific and different from "cut the stiles," even though both are just boards until they're assembled into their respective positions.