This is a post by Cat McClintock on PTC site.
Additive manufacturing (AM), also called 3D printing, is a method of creating physical objects layer by layer. Hobbyists and manufacturers alike have embraced AM because it can produce one-off objects without the upfront time or expense that high-volume manufacturing requires. In fact, it’s been especially useful for producing prototypes to test designs. Some also find AM helpful for creating hard-to-find replacement parts (think vintage cars).