Means "kneaded butter"; it is a paste made of softened butter and flour used to thicken sauces.
Beurre manie is a paste made from well-blended equal parts of softened butter and flour. It is used as a thickening for sauces and stews.
A butter and flour mixture used as a thickening agent. Basically uncooked roux, beurre manie is better used to thicken sweets, custards, etc.