What is the X in X-mas?
(Or "tractor feed", "pin feed") A method some printers use to move paper by rotating wheels with pins or studs (tractors) that engage holes along the sides of the (usually fanfold) paper. A sprocket feed printer does not slip unless the paper jams, but cannot feed standard typing paper or work with a sheet feeder like friction feed.
Some paper for sprocket feed printers has the edge strips with the holes in detachable from the rest of the paper. These strips are known as chad (and other names).