Avoidant personality disorder refers to an enduring pattern of social discomfort, fear of negative evaluation, and timidity.
People with this disorder tend to be socially isolated outside of family circles. They want to be liked by others, but they are easily hurt by even minimal signs of disapproval from other people.
Other definition:
Avoidant Personality Disorder refers to a Personality Disorder whose most prominent feature is that the person have desires, but is fearful of, any involvement with other people and is terrified at the prospect of being publicly embarrassed.
People with an Avoidant Personality Disorder exhibit, in a variety of contexts, a pervasive pattern of social inhibition, feelings of inadequacy, and hypersensitivity to negative evaluations or criticisms.
It is one of the Personality Disorder listed in Cluster C - disorders involving anxiety and fearfulness of the DSM-IV