I think a rotary is what you expect it to be... a shaver with rotating blades... just like many of those Norelco ones... the foil i belive is two perpendicular... sometimes just one piece of aluminum cover with grilles or little teeny weeny holes that have a vibrating blade under it. I would get the rotary one if i were you... those foil thing hurt sometimes since it doesn't cut off the stub smoothly... just zipping by back and forth like crazy. Ugh.