What is the difference between 2D and 3D milling?

The difference between 2D milling and 3D milling lies largely on the amount of machine axes that can be commanded on each line of NC code. Typically, when 2D milling, only the x- and y- axes will be utilized on a given move at the machine. In contrast, a simultaneous x-, y- and z-axis move can be used when 3D milling. For example, in complex surface machining, like you would find in mold and die components, Mastercam Mill 3D could be used to program any free-flowing complex surface or set of surfaces.