In medicine abnormality generally refers to a lack of integrity in any organ’s structure or function. A broken bone, an excess of certain sugar in the blood, an ulcer on the wall of the stomach-all are abnormal.
For physicians, the line between normality and abnormality is relatively easy to draw.

For psychologists and psychiatrists, however, the criteria that divide normal behavior from abnormal behavior are not easily specified, and several definitions of abnormality are used, each based on a different theoretical orientation. As well  there are several ways of defining psychological abnormality, and some of these definitions may change from one society to another and from time to time in the same society.