"In order to describe happiness, psychologists commonly refer to subjective well being (Kesebir & Diener, 2008). In other words, happiness is “people's evaluations of their lives and encompasses both cognitive judgments of satisfaction and affective appraisals of moods and emotions.”   https://positivepsychology.com/

"It’s only recently that we realized we could marry one of our oldest questions—“What is the nature of human happiness?”—to our newest way of getting answers: science. Until just a few decades ago, the problem of happiness was mainly in the hands of philosophers and poets. - Harvard psychology professor Daniel Gilbert"  https://hbr.org/