To scald milk: Place the milk into a saucepan on medium temperature and heat just until it starts to boil. Immediately remove from stove and set aside.
In the case of soups or some sauces: Scalding the milk will help prevent it from curdling.
This information is explained in the first paragraph under "Preparation" for the Sweet Tomatoes' Clam Chowder recipe IcyMist posted for you in the Soup Thread you started.
In the case of bread: Scalding kills a protein which causes a reduction in volume - a protein which is present in both raw/pasteurized-homogenized fresh and powdered non-fat dry milk.