What characteristic defines a whiskey that is served neat?

A whiskey served neat is characterized by being poured directly from the bottle into a glass without any additives like ice, water, or mixers. This means it is served at room temperature, allowing the drinker to experience the full range of flavors and aromas as intended by the distiller. Serving whiskey neat preserves the integrity of its taste profile and showcases the nuances of different whiskeys.

Options such as serving with ice, chilling, or providing a chaser alter the whiskey's temperature and flavor, which deviates from what neat whiskey is meant to represent. Hence, the fundamental aspect of whiskey served neat being at room temperature without any modifications is what makes this choice the correct one.