abnormal psychology

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun The study of mental and emotional disorders or maladaptive behaviors, or of mental phenomena such as dreams, hypnosis, and altered states or levels of consciousness.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun The academic study of persons whose psychological characteristics deviate from the norm, as with neuroses, psychoses, and disorders
• noun An instance of a person having psychological characteristics that deviate from the norm.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun the branch of psychology concerned with abnormal behavior