Milling is the process of machining by using rotary cutters to remove material from a work piece.  This is accomplished by using a cutter with many teeth spinning at high speed and advancing the material through the cutter slowly, or with the cutter being moved along the work piece perpendicular to its rotational direction.  The speed at which the piece is advanced through the cutter is called the feed rate.  The rotational speed of the cutter and the feed rate are varied depending on the type of material being worked and the type of cutter used.