In simplest terms, to tell a computer to "render" is telling the computer to "draw the information I've given you so far." Projects, whether still or animations are not complete until they have been rendered. ALIVE Studios offers a wide range of 3D Architectural Rendering & Architectural Visualisation services to help market your vision.
Rendering is the final front end and the product of the 3D process. In general terms, your 3D application is rendering all throughout the work process. The wireframe or shaded OpenGL view of your model that you work with is a sort of rendering.
However, most "feedback-based" renderings do not incorporate some very important specifics like reflections, shadows, and true transparency. The big rendering engines most commonly used today are Phong, Gouraud, raytracing, radiosity, toon, and other stylized rendering engines. Phong and Gouraud shading are some of the first rendering engines available and are typically very fast rendering processes.
They are so fast, in fact, that some applications like 3D applications use Gouraud shading as their feedback rendering engine; that is, they render fast enough to be interactive. A big drawback of these engines is that they typically use a scaled-back form of rendering transparency and never take into account any sort of refraction.
Further, most Phong and Gouraud shading shows the effects of light, but not their shadows (there are some forms of Phong shading that are exceptions to this rule). Some applications such as ElectricImage use a very fast form of Phong shading that will calculate refraction, shadows, and, with some tweaking, reflection.