4d graphics pretty much reffers to interactive and reactive spatial 3D animation, the fourth dimension being time.
Traditional 3d animation has static objects that you model and keyframe. There are some Hybrid systems that incorperate dynamic simulations with rigid and soft bodies, along with keyframed animations, which is then baked out into a sequence (see the destruction sequences in Halflife2 episode 2 for a good practical example of this)
True 4d graphics react in real time to everything around them, and is used for research into things like dynamics, chaos theory, fractal geometry and physics.
No flux capacitor required!
Source:
Emerging 4D Graphics for Math and Science Education
Ralph Abraham, Visual Math Institute, Inc.
and UC Santa Cruz
Michael Miller, The Enter Network, Inc.
John Miller, The Enter Network, Inc.