mental health

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A state of emotional and psychological well-being in which an individual is able to use his or her cognitive and emotional capabilities, function in society, and meet the ordinary demands of everyday life.
• noun A person's overall emotional and psychological condition.
• noun A field comprising various professions, such as psychiatry and social work, that deals with the promotion of mental and psychological well-being and the prevention, diagnosis, or treatment of mental disorders.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun One's emotional well-being, especially with reference to one's outlook on life, ability to cope with stress or the absence of a mental disorder.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun the psychological state of someone who is functioning at a satisfactory level of emotional and behavioral adjustment