It is the class name. It refers to the TOP (fastest/quickest) class running FUEL (i.e. mostly Nitromethane), not gasoline or alcohol. The cars are the long skinny ones usually called “rails”. There is an alcohol fueled version called "Top Alcohol Dragster with similar engines and design but running the safer and easier on engines methanol. They probably make 3500 hp these days instead of the Top Fuel cars 10,000 hp
FYI, Funny Car got its name because early ones had relocated rear axles for better traction and they looked kinda “funny”