As in “clarify” a consommé. The process of removing impurities from a stock or sauce (or butter). Egg whites, chopped vegetables, and lean meat (or fish) are introduced while the liquid is cold, then agitated with a whisk and slowly brought to a gentle simmer. If done right, the egg whites and other ingredients rise to the top and form a “raft,” bringing along any specks, scum, and impurities with them. The “raft” is then delicately removed before the liquid is strained, leaving behind a flawlessly clear, clean product. If you haven’t done this before, and are trying it for the first time, all I can say is good fucking luck.