Skybox
Refers to a design process where we have a [see page 18, large cube] with a fixed texture per-face to represent our scene. We place a synthetic object within this scene and use the outer worlds texture to calculate the reflections for environment-mapping.
The general idea is rather than calculating a texture to put around the object, construct a scene with a texture you already have and use that for object reflections.
This approach works well with static objects (those that can be deformed, but not moved around the world) but to move it around the world you'll need to recalculate the world texture for each frame of the animation.