Gidon, thank you.
Gary, a render engine is an application that creates the more or less realistic computer images you find in all sorts of places. Render engines can work out shadows and reflections and even the way light would behave as it passes through a material such as glass or water.
Although it probably isn't that useful for a woodworker who just wants to create some working drawings to build from, it is nice to show a client if you need to. Take a look at the recent entry in the CAD Gallery thread. There's a couple of pretty amazing images from a renderer. If you didn't know better you'd almost think they were photographs of real furniture.