An inferiority complex is an intense feeling of inadequacy, often resulting in excessive over-compensation, based on the belief that one is less than others in some way.
Related terms
Self-esteem: One's overall sense of self-worth or personal value.
Overcompensation: A defense mechanism when someone perceives a characteristic as being deficient, so they compensate by going overboard in another area.
Impostor Syndrome: The idea that you've only succeeded due to luck, not because of your talent or qualifications.