Fear is an unpleasant feeling of perceived risk or danger, real or not. Fear also can be described as a feeling of extreme dislike to some conditions/objects, such as: fear of darkness, fear of ghosts, etc. It is one of the basic emotions.
Fear may underlie some phenomena of behavior modification, although these phenomena can be explained without adducing fear as a factor in them. Furthermore, application of aversive stimuli is also often ineffective in producing change in the behaviour intended to be changed. Fearing objects or contexts can be learned; in animals this is being studied as fear conditioning, which depends on the emotional circuitry of the brain.
Fear inside a person has different degrees and varies from one person to another (see also phobia). If not properly handled, fear can lead to social problems. People who experience intense fear have been known to commit irrational and/or dangerous acts.
Some philosophers have considered fear to be a useless emotion with uniformly bad consequences; other thinkers note the usefulness of fear as a warning of bad situations.http://en.wikipedia.org/wiki/Fear