Whole milk powder (aka: powdered milk) is simply whole milk (although it can be found in all types - 2%, skim, etc.) that's been pasteurized, dried through evaporation, and then packaged in powdered form. It can generally be found in boxes, plastic jars, and even bags in the baking section at your local grocery. Take note that there's a texture difference between milk powder and instant powdered milk - the instant version tends to be grittier.