A neutral calcium carbonate ground to a fine powder. This is an ingredient in gesso and traditional paints such as distemper and is often used as a substitute for pounce powder. This recipe is recommended to make your own gesso: (25% whiting, 25% rabbit skin glue, and 50% water).
In intaglio printmaking whiting powder has several applications including plate wiping and plate degreasing. Mixed to a gloopy paste on the plate with ammonia or white vinegar, it is ever so slightly abrasive and will remove dirt and greasy finger marks before applying acid-resistant grounds and stop-outs.
In hand wiping, like French chalk, a tiny amount on your palm, excess removed, will aid with the final hand wiping of your plate, bringing up the highlights.