In the wonderful world of film, previsualization or pre-vis usually refers to using something to previsualize the visual flow of your film (shots, angles, etc.) before you actually start shooting.
Storyboarding is previsualization. A series of drawings showing, essentially, what the camera will see. Various machinima tools can also be used for pre-vis, and often are, from the kind of stuff we use (The Movies, iClone, Moviestorm, etc.) to specific pre-vis programs and even 3D modeling programs, from Blender to Maya and 3DMax.
Here's a good link that explains pre-vis and some of the tools that filmmakers use. http://wolfcrow.com/...re-and-methods/
Take any film on TMU and imagine it to be a pre-vis of a live action film. With something like that, you can see what works, what doesn't work - and you can share it with your team (actors, cinematographer, camera people) to show what you want each filmed scene to look like.