What constitutes abnormal behavior and the major models of abnormal behavior and their associated symptoms?

Answer 1

To understand what "abnormal" means, first consider "normal". Normal simply means average. People who behave normally are those who act and behave in an average, typical way. Statistically speaking, normal behavior is that which we would expect from the majority of people. Abnormal, therefore, refers to any behavior that is not typical. In the practice of psychology it has further come to mean mental illness.

It can present symptoms which are disturbing to both the sufferer and others: hallucinations, delusions, confused thought and speech, inappropriate emotions, strange gestures, and so on.