If you attach wheels to a tripod, you have a "dolly." In fact, any camera mount that has wheels is called a dolly.

You may have seen sophisticated dollies (and tracks) in one of those "making of" programs—they are used in feature films a lot.

Upper right: This super-simple dolly attaches to the bottom of a tripod so you can roll it around. Lower right: A much-more sophisticated dolly offers very precise controls--and a place for the camera operator to sit.