Well-being, or wellbeing, also known as wellness, prudential value, prosperity or quality of life, is what is intrinsically valuable relative to someone. So the well-being of a person is what is ultimately good for this person, what is in the self-interest of this person. Well-being can refer to both positive and negative well-being. In its positive sense, it is sometimes contrasted with ill-being as its opposite. The term "subjective well-being" denotes how people experience and evaluate their lives, usually measured in relation to self-reported well-being obtained through questionnaires.

Quality of life (QOL) is defined by the World Health Organization as "an individual's perception of their position in life in the context of the culture and value systems in which they live and in relation to their goals, expectations, standards and concerns".