In architecture, 3D printing is a three-dimensional construction process that extrudes various mixtures of materials in the texture of concrete — or firm mud — in layers to construct walls. The layers look like dough extruded through a pasta maker or a cookie press. The process requires huge machines guided by a digital file in which the shapes and dimensions have been defined. The result can be much more elegant than the name.
The creation of a 3D printed object is achieved using additive processes. In an additive process, an object is created by laying down successive layers of material until the object is created. Each of these layers can be seen as a thinly sliced cross-section of the object. As 3DPrinting.com explains it:
3D printing is the opposite of subtractive manufacturing which is cutting or hollowing out a piece of metal or plastic with, for instance, a milling machine. 3D printing enables you to produce complex shapes using less material than traditional manufacturing methods.
(There should be something more descriptive than printing. Typically, printing is a process of applying ink or paint to a 2D surface, usually to paper or fabric. Additive is perhaps better but still not quite right. Additive printing doesn’t work. It’s the printing that bumbles things up for anyone familiar with printing.)