To combine a light mixture with a much heavier mixture. An example is beaten egg whites combined with a cheese sauce as in making a cheese soufflé.
Place the heavier mixture in the bottom of a large bowl. Add the lighter mixture and, using a rubber spatula, scrape along the outer edge of the bowl turning the heavier mixture gently over the top of the lighter. Turn the bowl and repeat until the two are well combined. The goal is to gently work the two together without beating down the lighter mixture.