A treadle is a sewing machine that's mounted in a cabinet with a foot pedal that you manually pump.
I'll try to find a photo. Here is a photo of my treadle. It is a model 27. If you need help indentifying the model of machine you have, you can use this website (
http://www.sandman-collectibles.com/...achines.htm#14) to help you figure it out.