Creaming is used to refer to several different culinary processes.
Blending to a creamy mass
Creaming, in this sense, is the technique of blending several ingredients — for example granulated sugar together with a solid fat like shortening or butter — and working them to a smooth mass. The technique is most often used in making buttercream, cake batter or cookie dough. The dry ingredients are mixed or beaten with the fat until it becomes light and fluffy and increased in volume, due to the incorporation of tiny air bubbles. These air bubbles, locked into the semi-solid fat, remain in the final batter and expand as the item is baked, serving as a form of leavening agent.
Butter is the traditional fat for creaming batter for baking, but vegetable shortening is a more effective leavener for a number of reasons. The low melting point of butter means it aerates best at temperatures cooler than most kitchens (18 °C/65 °F), while shortening works best at higher temperatures. Because fat of butter has coarser crystalline structure, it allows larger air bubbles to form than shortening; large bubbles can rise in and escape from thin batters. Also, most shortening is made with preformed nitrogen bubbles and bubble-stabilizing emulsifiers, both of which enhance its leavening ability.
Cooking creamed food
Some commercial preparations of "creamed" food substitute water and a starch (often corn starch) for all or some of the milk or cream. This produces a "creamy" texture with no actual cream or milk used.