One of the four "mother sauces" (see sauce), velouté is, in the most basic terms, a white stock thickened with white roux. It is the foundation for myriad sauces and can be flavored in infinite ways. For example, allemande sauce is an egg-enriched velouté.
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.