Potato starch refers to the powdered form of starch extracted from potatoes. It is used as a thickening agent in cooking and baking, similar to flour or cornstarch. Full definition
If you are out of potato starch use more corn starch or tapioca starch instead. (eatthelove.com)
I use a recipe calling for 2 cups white rice flour, 1/2 cup tapioca flour, 1/2 cup potato starch, and 1/3 cup cornstarch. (petiteallergytreats.com)
Don't confuse potato flour with potato starch, which is used in much larger quantities in recipes and has different baking properties. (glutenfreeandmore.com)