Emotion refers to a state characterized by physiological arousal, changes in facial expression, gestures, posture, and subjective feelings ; a pattern of action elicited by an external
event and a feeling state, accompanied by a characteristic physiological response.
Moreover, Emotion is a subjective state of positive or negative affect often accompanied by a degree of arousal or activation; a motivational construct that is characterized by changes in affect (or feelings), physiological responses, cognitions, and overt behavior.
Emotions are emotional experiences which are usually more intense and shorter lasting than moods.
There are several theories of emotions, among the classic ones are:
1. James-Lange Theory
2. Cannon-Bard Theory
3. Schachter-Singer Theory
4. Lazarus Theory
5. Facial Feedback Theory
Other /More definition:
emotion refers to the pattern of action elicited by an external event and a feeling state, accompanied by a characteristic physiological response.