1. When it coagulates, milk separates into a semisolid portion (curd) and a watery liquid (whey). It's the addition of rennet to the milk that makes the individual milk protein (casein) cells clump together to form the curd mass, from which cheese is made. 2. A creamy mixture made from juice (usually lemon, lime or orange), sugar, butter and egg yolks. The ingredients are cooked together until the mixture becomes quite thick. When cool, the lemon (or lime or orange) curd becomes thick enough to spread and is used as a topping for breads and other baked goods. Various flavors of curd are available in gourmet markets and some supermarkets.
From The Food Lover's Companion, Fourth edition by Sharon Tyler Herbst and Ron Herbst. Copyright © 2007, 2001, 1995, 1990 by Barron's Educational Series, Inc.