Abnormality is a subjectively defined characteristic, assigned to those with rare or dysfunctional conditions. Defining who is normal or abnormal is a contentious issue in abnormal psychology.

There are several conventional criteria .

One simple criterion is statistical infrequency. This has an obvious flaw — the extremely intelligent, honest, or happy are just as abnormal as their opposites.

A more discerning criterion is distress. A person who is displaying a great deal of depression, anxiety, unhappiness, etc. is defined to be abnormal. Unfortunately, many people are not aware of their own mental state, and while they may benefit from help, they are feel no compulsion to receive it.

Another criterion is morality. This presents many difficulties, because it would be impossible to agree on a single set of morals for the purposes of diagnosis.

One criterion commonly referenced is maladaptivity. If a person is behaving in ways counterproductive to their own well-being, it is considered maladaptive. While tighter than the above criteria, it does have some shortcomings. For example, moral behavior including dissent and abstinence may be considered maladaptive.

The standard criteria in psychology and psychiatry is that of mental illness. Determination of abnormality is based upon medical diagnosis. This is often criticized for removing control from the 'patient', and being easily manipulated by political or social goals.