white sauce

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A sauce made with butter, flour, and milk, cream, or stock, used as a base for other sauces.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun A simple sauce made from flour, milk and butter
• noun mayonnaise

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun milk thickened with a butter and flour roux