Behaviour that is seen as deviating from the rules regulating how one should behave is seen as undesirable by the majority of society's members.
Failure to function adequately:
This refers to abnormality that would prevent the person from carrying out the range of behaviours that society would expect from them, such as being able to get out of bed each day or holding down a job. Rosenhan and Seligman suggested a range of criteria that are typical of FFA. These include observer discomfort, unpredictability and irrationality amongst others.
Statistical Infrequency:
The idea here is that behaviours that are statistically rare should be seen as abnormal
Deviation from ideal mental health:
Defining what is normal and ideal mental health and everything that deviates from this is abnormal