POV-Ray is a full-featured ray tracer. Ray tracers simulate objects and light sources of the real world to calculate photorealistic, computer generated images. Because of the nature of ray tracing, this process is quite CPU-intensive, at the benefit of more realistic images compared to real time rendering techniques. For example, in POV-Ray, you can model a glass prism, and you will see a spectrum in the resulting image.
POV-Ray by itself is a command-line utility that will take scene descriptions, written in a special easy-to-understand language, to produce ray-traced images (or even a sequence of images, for animations). You can either write those scene-descriptions by hand, or use external tools to generate (parts of) the scene.
povray-includes is highly recommended in addition to this package.