3D Printing is currently rather a hard term to define. Officially it is just one of the rapid manufacturing techniques. Currently however the term 3D Printing itself is used as a synonym for rapid manufacturing, digital manufacturing, direct digital manufacturing, rapid prototyping, desktop manufacturing, freeform fabrication and fabbing.
Each one of these terms has a distinct meaning but they are all vying for your attention to become the official term to describe any process whereby the information in a digital file describing an object virtually(such as an STL or CAD file) is used to rapidly make a real object. Usually by one single machine and usually in limited production runs.
The official definition maintains that 3D Printing is is just one of the many ways that you do this. In that light: 3D Printing is a technique that deposites material layer by layer using a head similar to that of a inkjet printer. The head tends to move along the X and Y axes and the object being printed moves up and down on the Z axis. In the picture above you can see our Objet printer at work. The head is printing two copies of Macouno's Shapeways model Petunia(Of Project Petunia fame). The two Petunias are on a base plate that moves down along the Z axis to give the model depth.
At Shapeways we have noticed that we, our designers and partners tend to use 3D Printing as a general term to describe any rapid manufacturing technique. In a future post I will try and clear up some of the differences between the different techniques and materials.I hope that this definition helped, and did not confuse.
Although the RepRap has been getting all the press lately, for me Fab@Home Project is the original open source, cheap, desktop 3D Printer project.