Culinary definition of sift: sifting is to pass dry ingredients through a fine mesh sift or sieve to filter out large pieces, to separate and add air.
C@H FOOD FOR THOUGHT
There was once an assumption that flour was to be sifted before measuring, and that all dry ingredients used in baking were to be sifted together. Vintage cookbooks say as much. Not so today however, as recipes and cook books are as unique as their authors.
It is a good idea when baking at least, to sift flour together with other dry ingredients like baking powder, fine salt and ground spices. Sifting adds air, evenly distributes ingredients and is a lovely and tactile thing to do. Sifters come in a variety of shapes and sizes, so it makes sense to have a few on hand; one footed, one large and one small.
A large sieve with hooks on the rim - opposite to the handle - allows you to rest the sieve over a mixing bowl of pot and keep your hands free. Be sure to purchase only stainless steel sifters/sieves as steel will rust quickly. See also Sieve