What's the difference between “intermodal” and “rail”?

Intermodal is a subset of rail and involves the movement of highway-capable units, either containers or trailers, on special intermodal railcars.

Intermodal is a subset of rail.  Rail includes “carload” movements, which would be things like boxcars, hopper cars, etc.  Intermodal movements, on the other hand, involves the movement of highway-capable units, either containers or trailers, on special intermodal railcars.