A walking foot is a special type of machine. The foot has two pieces. The material is always being moved through the machine.
http://www.ebay.com/itm/Sailrite-LSZ...-/110970290157 here is some sewing machine with one - scroll down to see the foot - it looks like 3 toes the middle one and then on each side of it The foot moves pulling fabric through as well as the feed dogs. Not good for FM...