Roux

A cooked mixture of equal parts fat and flour used to thicken sauces.

What it means in a kitchen

Roux is the structural backbone of béchamel, velouté, and gumbo. The longer you cook it, the darker and more flavorful but also the less thickening power it retains. White roux for delicate dishes, blond roux for stocks, brown roux for stews — the same ratio, different cook times.