Also called dry rub, a rub is typically a mixture of herbs and spices (and usually salt) that is spread over the outside of meat, fish and sometimes even vegetables a few hours before cooking. This blend may be completely dry or mixed with a small amount of liquid to achieve a pastelike texture. Rubs infuse foods with flavor, which intensifies during cooking (usually barbecuing, grilling or roasting). Sugar added to the rub caramelizes with heat, adding a deep rich color and flavor.
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.