What is the main characteristic of a soufflé?

A soufflé is primarily known for its light and airy texture, which is achieved by incorporating beaten egg whites. When egg whites are whipped, they trap air, allowing the soufflé to rise as it bakes, creating a delicate and fluffy consistency. This characteristic is fundamental to the soufflé's identity, distinguishing it from other dishes that might be denser or heavier.

The other options do not define a soufflé accurately. While some variations of soufflés can be served cold, they are typically enjoyed warm or hot right out of the oven, which is crucial to maintaining their texture. Describing a soufflé as dense or heavy contradicts its primary nature of being light and airy. Additionally, while chocolate soufflés are popular, a soufflé can be made in various flavors, including cheese and fruit, so it does not always contain chocolate. Therefore, the defining trait is indeed its light, fluffy nature produced by the method of incorporating beaten egg whites.