Definitions of abnormality- deviation from social
Deviation from social norms: all socities have their standards of behaviour and attitudes. Deviating from these can be seen as abnormal. But some cultures vary, so there isn't one universal set of social 'rules'. One problem with defining abnormality as deviation from social norms is that it can be used to justify the removal of 'unwanted' people from a society. For example, people opposing a particular political regime could be said to b abnormal.
Weaknesses: it is susceptible to abuse. What is socially acceptable now may not have been acceptable 50 years ago. E.g. homosexuality is acceptible today although 50 years ago they were seen as insane and placed into a mental institution. It depends on time and place to determine what is socially acceptible, therefore not reliable.
Cultural relavitism: different cultures may percieve disorders as norms according to their society. E.g. in some eastern cultures sacrificing a child for their "gods" whereas in western cultures like British society it is seen as insanity.
Failure to function adequately
When an individual can't cope with the demands of day-to-day life.