What is 3D printing?

There is a lot of talk about how 3D printing could revolutionise the way that we make stuff. But what is 3D printing and how does 3D printing allow us to make almost anything from nothing? Head of the Institute for Manufacturing, Professor Tim Minshall, explains in this video, which is targeted at school-age students, that there are four different processes for making things and how 3D printing could be used in the future to make new shapes that were previously not possible.