A state of being that is relative rather than absolute. The best indices of mental health are simultaneous success at working, loving, and creating, with the capacity for mature and flexible resolution of conflicts between instincts, conscience, important other people, and reality.
Having all our mental and emotional processes functioning in ways which enable us to make quality relationships and have quality of life. The term developed from the mind-body split which underlay western philosophy and science for 400 years. Just as there is physical health, so it was assumed there is mental health. While there are clearly some conditions which relate to brain functioning, the distinction between mental and physical health is increasingly being recognised as unhelpful though it is unlikely that we will have a new term in the immediate future.
As well as acute and chronic conditions, such as schizophrenia and clinical depression, it includes dementia, and other mental health problems of older people, and problems arising from misuse of drugs, alcohol or other substances.