1. the study of the mind and behavior. Historically, psychology was an area within philosophy and emerged from it (see epistemology). It is now a diverse scientific discipline comprising several major branches of research (e.g., experimental, biological, cognitive, lifespan developmental, personality, social), as well as several subareas of research and applied psychology (e.g., clinical, industrial/organizational, school and educational, human factors, health, neuropsychology, cross-cultural). Research in psychology involves observation, experimentation, testing, and analysis to explore the biological, cognitive, emotional, personal, and social processes or stimuli underlying human and animal behavior. The practice of psychology involves the use of psychological knowledge for any of several purposes: to understand and treat mental, emotional, physical, and social dysfunction; to understand and enhance behavior in various settings of human activity (e.g., school, workplace, courtroom, sports arena, battlefield); and to improve machine and building design for human use.

2. the supposed collection of behaviors, traits, attitudes, and so forth that characterize an individual or a group (e.g., the psychology of women). —psychological adj.