Ray-tracing is a method for depicting three-dimensional objects realistically. It is computationally expensive, because it requires a separate computation for each pixel on the screen.
The ray-tracing technique can be used to handle many objects at once and many lighting sources. The objects can reflect light like a mirror (specular reflection), or diffusely like paper (diffuse reflection), or they can be transparent and refract (bend) light like glass, or a combination. The light can come from nearby sources or sources at infinity, it can be of any combination of colors. A perspective view is usually used.