A "body scan" can refer to several things, most notably it is an X-ray-based technology that produces a high-resolution image of a person's body beneath their clothing (in order to reveal concealed objects). This process (also known as "backscatting") has been used in prisons, diamond mines, and customs searches, and it is being tested as an alternative to metal-detection and pat-downs for airport security.
Another definition of a "body scan" involves the process of using a life-size scanner to scan your body in order to have a better-fitting pair of pants, custom made to your exact size. It involves a scanning booth, the light scan (which takes about 12 seconds), and a software program to record an individual's precise measurements. These measurements are then fed into a database that can be accessed over the Web by you and/or an online clothes etailer. This particular technology is available but not yet widely used; companies that manufacture body scan booths also intend to use this technology to fit individuals with prosthetics or ergonomic devices.
Finally, there is another type of "body scanning" which refers to a medical procedure (similar to a CAT scan but it is for the entire body.)