The understanding of the concept of health is unlikely to be complete without the overview of the related states of disease or disorder. This not only introduces a newer concept but also helps to understand the concept of health better. The traditional approach of defining disorder as a deviation from the health state makes it essential to appraise oneself with this rather extensively studied concept. The term disorder represents the conjunction of a syndrome with a clinical course. 
2.1 Defining Mental Disorders
Mental disorder is a commonly used term in the field of mental health. The safest understanding of this term would be as a term used to define something that is dysfunctional or unhealthy. The word safest has been used here to highlight those different meanings are ascribed to the term mental disorder. This lack of uniformity results from the lack of definitive etiological understanding of mental disorders. Simply speaking, mental disorders could be seen as disorders of the conation (action), cognition (thought) or affect (feelings). Before we proceed to the definition of mental disorders, we do need to keep in mind that no single definition adequately specifies precise boundaries for the concept of mental disorder.
As per the Diagnostic and Statistical Manual (DSM)-IV (a diagnostic system developed in USA and used in different countries), mental disorder is a psychological or behavioural pattern that is associated with present distress or disability or with a significantly increased risk of suffering death, pain, disability or an important loss of freedom. It must currently be considered a manifestation of a behavioural, psychological or biological dysfunction in the individual.
To better understand this seemingly comprehensive definition we can cite the example of an individual who is experiencing a set of clinical features including the depressed mood, ideas of helplessness, decreased appetite and fragmented sleep leading to absenteeism from job. From our personal experiences we can tell that the fluctuations of mood, sleep and appetite have been experienced by all of us at least at some point in time.