The theory of value, also known as axiology, studies what kind of things and outcomes are morally good, or intrinsically valuable. This is in contrast to the theory of the right, which studies what people morally ought to do.

https://concepts.effectivealtruism.org/concepts/theories-of-value/

Well-being is what is good for a person, or what makes their life go best. It is generally agreed that all plausible moral theories assign at least some value to well-being, with some - welfarist theories - holding that nothing but well-being has value.