What is the term for the appearance of observable emotions?

The term that describes the appearance of observable emotions is "affect." Affect refers specifically to the external expression of emotions, which can be observed in a person's posture, facial expressions, and tone of voice. It represents how a person presents their emotional state to others, often referred to as the affective component of emotional responses.

In contrast, the other terms hold different meanings. "Emotion" pertains to internal feelings that a person experiences but does not specifically refer to their outward expression. "Sentiment" typically relates to a more general attitude or opinion, not necessarily tied to immediate emotional displays. "Mood" describes a more lasting emotional state that might influence affect but is not synonymous with observable expression. Therefore, the correct term for the observable manifestation of emotions is clearly defined as affect.