Broadly speaking, there are two meanings. Firstly, it is the scientific study of aberrant behaviours and mental disorders, and secondly it constitutes the collective signs and symptoms of a mental disorder. It is held that psychopathology should not be equated with psychopathy, the latter concerning anti-social personality disorders as well as criminality.
See Diagnosis (or diaeresis), Pathophysiology, Pathogenesis (or pathogeny), Signs and symptoms