There may be. The mustard processors of the world have not yet settled on a definitive naming scheme for their products.

Theoretically dry mustard and powdered mustard and ground mustard are the same thing. You might find some variation in the fineness or coarseness of the grind. There are certain brands that label their mustard powder as "double superfine," which is very finely ground.

But we have also stumbled across some manufacturers who refer to their prepared mustard as "ground mustard" or "stone-ground mustard" to differentiate it from whole-seed or cracked-seed prepared mustard and to differentiate it from mustard ground by steel rollers.

Recipes calling for dry mustard, powdered mustard, or ground mustard should be asking for the same thing – dry, finely ground mustard.