In Philosophy, Happiness is translated from the Greek concept of Eudaimonia, and refers to the good life, or flourishing, as opposed to an emotion.
In Psychology, happiness is a mental or emotional state of well-being which can be defined by, among others, positive or pleasant emotions ranging from contentment to intense joy.
Happy mental states may reflect judgements by a person about their overall well-being.
Positive Psychology is:
"The Scientific study of what makes life most worth living", or "the scientific study of positive human functioning and flourishing on multiple levels that include the biological, personal, relational, institutional, cultural, and global dimensions of life".
Positive psychology is concerned with eudaimonia, "the good life", reflection about what holds the greatest value in life the factors that contribute the most to a well-lived and fulfilling life.