Abnormal behavior is defined as

a. pattern of thoughts that are not common

b. pattern of behavior passed on through families

c. pattern of thoughts that can lead to a problem

d. pattern of behavior that causes people significant distress

The correct answer is d. pattern of behaviour that causes people significant distress. People usually confuse abnormal behavior with unusual behavior, but behaving in a way which out of the ordinary does not necessarily mean that a person suffers from a mental or psychological disorder. Abnormal behavior is often indicative of mental and psychological disorders. According to the The Encyclopedia of Clinical Psychology, a psychological disorder is defined as an "ongoing dysfunctional pattern of thought, emotion, and behavior that causes significant distress, and is considered deviant in that person's culture or society".