According to the World Health Organization, mental health is “the state of wellbeing in which every individual realizes [their] own potential, can cope with the normal stresses of life, can work productively and fruitfully, and is able to make a contribution to [their] community."
Source: "10 facts about mental health", World Health Organization, 2019. https://www.who.int/news-room/facts-in-pictures/detail/mental-health