Answer:
A wide range of mental conditions that affects the mood of the person, behavior of the person and thinking of the person is called as mental disorder.
Example: Clinical depression: It is characterized by constantly a depressed mood or loss of interest in the activities causing an impairment in the daily life of the person.
The mental illness is also a type of mental disorder which is characterized by a sad mood and depressed mood for a longer period of time.
Example: Schizophrenia