Cream, as a verb (as opposed to the thousands of questions we get about cream as a noun), means to beat and mix an ingredient or a combination of ingredients to a smooth, creamy consistency. You'll see it most often in the case of butter and sugar, where the sugar is dissolved into the butter as the butter is softened.

Creaming ingredients by hand starts by mashing the ingredients up against the side of a mixing bowl with a spoon, fork or spatula, and beating and beating until the mixture is smooth and homogeneous. In many kitchens, an electric mixer and, to a lesser extent, food processor and blender have lightened the work load considerably.