From Power, M. (2010, pp. 18-19) [Emotion-Focused Cognitive Therapy, Wiley-Blackwell]:
Emotions are mental and bodily states that typically comprise a constellation of physiological, behavioural and psychological processes that follow the appraisal or evaluation of a situation or event as relevant to the individual’s goals. These goals range from basic drive-based survival goals to higher-order interpersonal and aesthetic goals. There are a limited set of such emotion states that include fear, sadness, anger disgust and happiness, all of which have come to signal in a multitask multilevel system shifts in the priority of goal-based functioning and from which an infinite range of more complex emotions are derivable. These emotion states are normally short-lived in nature and need only last a matter of seconds or minutes; when they become more chronic, they are normally referred to as “moods” for which the instigating situation or event may have been forgotten. The conscious aspect of an emotion is referred to as its “affect” or “feeling”, though under many circumstances emotions can be unconscious and have no reportable affect state.
[...] might also enjoy this lovely definition. (And this on problems with [...]