Psychology is the study of the way humans and animals interact and respond to their environment. The manner in which they do is called behavior.
Psychology combines humanities and science. Psychologists try to discover why certain people react to certain aspects of society and the world at large in a certain way, and from those reactions, they try to deduce something about the biology of our brains and the way the environment influences us. Sound complicated? It is, but it's also a profoundly fascinating major. If you major in Psychology, you'll look for the essence of why people are the way they are, from their personality type to their sexual orientation. Within this broad framework, Psychology majors focus on such features of the human mind as learning, cognition, intelligence, motivation, emotion, perception, personality, mental disorders, and the ways in which our individual preferences are inherited from our parents or shaped by our environment.
With a strong background in research and the scientific method, a Psychology major pursues a field of study that seeks to educate, communicate, and resolve many of the problems surrounding human behavior.