Final answer:
A roux is a thickening agent used in making sauces and soups, consisting of equal parts flour and fat cooked together.
Step-by-step explanation:
A roux is C) A thickening agent for sauces and soups. It is made by cooking together equal parts of flour with fat, such as butter until it reaches the desired color and aroma. The roux is used as a base for many dishes in classical French cooking and plays a significant role in cuisines around the world, especially in creamy or thickened sauces and stews. There are different types of roux-based on their cooking duration: white, blond, and brown, each providing a different depth of flavor and color to the dish they are used in.