Suppose you needed an object of a certain shape for a project. In the past, you'd have started with a block of material and removed the parts you don't need to arrive at the desired shape. That's "subtractive manufacturing" where you create a shape by removing material. If you think about it, you could also create that object by putting down the material a layer at a time, each layer with the needed shape. That, in essence, is 3D printing -- the method of creating a 3D object by laying down material a layer at a time. It's also called "additive manufacturing" because you add material rather than remove material. As you can see, this approach is less wasteful because you end up using exactly the amount of material you need.
3D printers are already available for people to buy and use. Here is an example -- the Makerbot Replicator -- that costs around two to three thousand dollars. The situation with 3D Printers is similar to when the PCs first became widely available in early to mid 1980s. If you are into it, you can now buy a 3D Printer and experiment with it, as many are already doing.
These printers use plastic filaments that are melted and laid down layer by layer to create a 3D object from a computer file that describes the object. The printer takes the 3D description and keeps putting down material layer by layer until the whole shape is created. You can create objects of any complexity with this approach. For example, using the old "subtractive" approach, it's quite difficult to create an object with some complex cavity inside of it, but something like that is simple to do with 3D printers.
Although most consumer 3D printers use plastic as the material, there are industrial 3D printers that can "print" objects using metals and other materials. General Electric, for example, is printing jet engine parts using 3D printers and whole cars have been printed using industrial 3D printers.
The example I used in the video showed an object created from paper and guess what, The Economist magazine had an article in its Aug 10th-016th, 2013 issue that talks about a 3D printer that creates 3D objects using paper!
That's 3D Printing in simple terms. Later I'll discuss why it's such a big deal.