A more difficult question to answer than one might think. As usual your definition depends on all or some of your point of view.
The term ‘health’ is a non-exact term used loosely in everyday speech. Equally ‘mental health’, ‘mental illness’ and ‘mental disorder’ are used with an comparable lack of precision and the latter two most often interchangeably. In addition psychiatric health/illness/disorder are used synonymously with mental health/illness/disorder. A further problem with this concept is that there is no clear cut off point between mental disorder and mental health; indeed one person’s mental health aid, might be another’ s mental disorder inducer.
The obsession Americans have for classifying and naming every single human behavior, body dysfunction, and other classifiable entities does not help the process of healing. But the most harmful misconception is that they consider that the classifications or illness do not overlap or interact with each other. This obsolet concept is the main cause of treatment failures.