In psychology, affect is used to describe the essence of a feeling or emotion. Affect is a simplified experience of an emotion. It has 2 main properties.
- Valence: How positive or negative a feeling is. Ranges from pleasant to unpleasant. Sadness is a negative Affect and joy is a positive Affect.
- Arousal: How energetic your feeling is. Ranges from calm to agitated. Feeling calm is low arousal and feeling anger is high arousal.
On the other hand, Emotion is a more complex concept involving motivation, specific feelings, details, physical state, unique reactions, etc. Affect and Emotions are both short-lived (less than a few minutes), but a mood is long-lasting (a few hours to days). Emotions involve bodily sensations and facial & bodily expressions. Affect is a stripped-down version of the emotion with a valence (+ve to -ve) and overall arousal (low to high).
However, researchers have used both words interchangeably across decades of research.
Mood, unlike emotions, is a global tendency to experiences a specific category of emotions more often over a long duration. A mood is subjective and contains a fairly inflexible mental state. Emotions and Affect are significantly different from the previous mental state. But it also has the properties of Affect.
For example, a low-mood can be negatively valenced with a high frequency of sadness, numbness, discomfort, etc. An agitated mood could have a high frequency of irritation, anger, and anxiety. So Mood has variability which describes the range and type of Emotions or Affect one experiences over time.