Fear is an emotional response to threats and danger. It is a basic survival mechanism occurring in response to a specific stimulus, such as pain or the threat of pain. Psychologists John B. Watson and Paul Ekman have suggested that fear is one of a small set of innate emotions. This set also includes joy, sadness, and anger.

Fear should be distinguished from anxiety, which typically occurs without any external threat. Additionally, fear is related to the specific behaviors of escape and avoidance, whereas anxiety is the result of threats which are perceived to be uncontrollable or unavoidable.

Etymology

The Old English term fǣr meant not the emotion engendered by a calamity or disaster, but rather the event itself. The first recorded usage of the term "fear" with the sense of the “emotion of fear” is found in a medieval work written in Middle English, composed circa 1290. The most probable explanation for the change in the meaning of the word "fear" is the existence in Old English of the related verb fǣran, which meant “to terrify, take by surprise”.

Varieties

Fear can be described using different terms in relation to its varying degrees. Personal fear varies extremely in degree from mild caution to extreme phobia and paranoia. Fear is related to a number of emotional states including worry, anxiety, terror, fright, paranoia, horror, panic, persecution complex and dread.

Fear may be a factor within a larger social network, wherein personal fears are synergetically compounded as mass hysteria.

• Paranoia is a term used to describe a psychosis of fear, described as a heightened perception of being persecuted, whether unfounded or otherwise. This degree of fear often indicates that one has changed their normal behavior in radical ways, and may have become extremely compulsive. Sometimes, the result of extreme paranoia is a phobia.

• Distrust, in the context of interpersonal fear, is sometimes explained as the inward feeling of caution, usually focused on a person; representing an unwillingness to trust in someone else. Distrust is not a lack of faith or belief in someone, but a feeling of warning towards someone or something questionable or unknown. For example, one may "distrust" a stranger who acts in a way that is perceived as "odd". Likewise, one may "distrust" the safety of a rusty old bridge across a 100-foot drop.

• Terror refers to a pronounced state of fear - which usually occurs just before the state of horror - when someone becomes overwhelmed with a sense of immediate danger. Also, it can be caused by perceiving a (possibly extreme) phobia. As a consequence, terror overwhelms the person to the point of making irrational choices and displaying atypical behavior.