Which culinary term describes a sauce that is thick enough to coat a spoon?

The term that specifically refers to a sauce thick enough to coat a spoon is "nappe." In culinary contexts, nappe refers to the consistency of a sauce or liquid that allows it to cling to the back of a spoon, indicating a certain thickness or viscosity. When a sauce has achieved this state, it indicates that it has been properly reduced or thickened, which is crucial for many recipes where a luxurious mouthfeel is desired.

In contrast, consommé refers to a clear soup made from richly flavored stock or broth that is clarified, and it does not imply thickness. Reduction describes the process of concentrating a liquid by boiling or simmering to evaporate some of the water content, which may lead to a thicker sauce, but does not specifically define the final consistency. Emulsion refers to a mixture of two liquids that normally do not mix, such as oil and vinegar, and while an emulsion can be thick, it does not inherently indicate a sauce that coats a spoon.

Thus, nappe is the precise culinary term used to communicate the ideal thickness that enables a sauce to adhere to a spoon, making it the correct choice.