So with 3D printing finally gaining main stream awareness I get a lot of requests to explain exactly what it is. People generally quickly get the slicking up a model into layers and building up the model a layer at a time. What tends to be harder to visualize is the use of support.
Support is used to support the print material during printing. It is then removed after printing is completed, enabling impossible looking parts to be printed. I think the best example is the artwork of Bathsheba (http://www.bathsheba.com).
What you see here are two pictures of the Metatron model, both with and without support. The support is the black material and it is dissolved away in a solvent tank. The white material the model is made from is just ABS plastic.
Some printers are built the model from a powder which is blown away once the model is done being printed – but most of the fused deposition modeling use this style of support.