3D scanning refers to a broad range of technologies that bring the physical world into the digital world. This a broader view than most would give you but I feel it is more appropriate because it encompasses technologies such as:
These technologies are similar in application and the technical skills required to develop them. I won't go into too much detail on the list above because there are more comprehensive sources such as http://en.wikipedia.org/wiki/3D_scanner.
I put together a very basic technical description of 3D scanning.