In behavior, normal refers to a lack of significant deviation from the average. The phrase "not normal" is often applied in a negative sense (asserting that someone or some situation is improper, sick, etc.) Abnormality varies greatly in how pleasant or unpleasant this is for other people.
The Oxford English Dictionary defines "normal" as "conforming to a standard". Another possible definition is that "a normal" is someone who conforms to the predominant behavior in a society. This can be for any number of reasons such as simple imitative behavior, deliberate or inconsistent acceptance of society's standards, fear of humiliation or rejection, etc.
The French sociologist Émile Durkheim indicated in his Rules of the Sociological Method that the most common behavior in a society is considered normal. People who do not go along are violating social norms and will invite a punishment from others in the society.