To understand the abnormal behaviour of a person, it is necessary to understand the meaning of the word normal and abnormal.
The word normal derives from the Latin word "Norma" which means the carpenter's measure tap. A carpenter's measure tap is an ideal measuring instrument and is considered perfect. So it can be said that ideal situation of the uniformly accepted norms is known as normal – Therefore
Abnormal = АВ + Normal Away from + Normal So, "Abnormal means away from normal."; It is difficult to say what type of behaviour is normal and which is abnormal as the concept of both type of behaviour varies in relation to age, caste, sex, society etc. For example : When a small child loses his pencil, he becomes violent and cries loudly which is considered normal, but if a 25 years old person loses his pen and does similar type of behaviour, it is considered abnormal.
Usually a normal behaviour means the behavior which is according to society, age, and culture and is corresponding to the social norms and social expectations and also adjusted to its environment is called as a normal behaviour. On the contrary, behaviour which is opposite to social norms and social expectations and maladjusted is known as abnormal behaviour.