In machining, 2.5D refers to a surface which is a projection of a plane into 3rd dimension – although the object is 3-dimensional, there are no overhanging elements possible. Objects of this type are often represented as a contour map that gives the height (i.e., thickness or depth) of the object at each point. 2.5D objects can be machined on a 3-axis milling machine, and do not require any of the features of a higher-axis machine to produce.