Psychology: The study of the mind and mental processes, especially in relation to behavior. There are a number of fields of psychology. Clinical psychology is concerned with diagnosing and treating disorders of the brain, emotional disturbances, and behavior problems. Child psychology is the study of the mental and emotional development of children and is part of developmental psychology, the study of changes in behavior that occur through the life span. Cognitive psychology deals with how the human mind receives and interprets impressions and ideas. Social psychology looks at how the actions of others influence the behavior of an individual.