3D printing is a process of making a three-dimensional solid from a digital model. 3D printing is achieved using an additive process, where successive layers of material are put down one at a time - the opposite of traditional machining in which material is taken away from a solid material to make a shape.
For an example, here is a 3-minute time lapse of a gear being "printed".
Bear in mind that this is sped up by a factor of eight, so printing this one little gear actually took about a half hour.
There are two 3D printers on campus - both are Stratasys Uprint SE Plus models.