Happiness is used in the context of mental or emotional states, including positive or pleasant emotions ranging from contentment to intense joy. It is also used in the context of life satisfactionsubjective well-beingeudaimonia, flourishing and well-being. 

Since the 1960s, happiness research has been conducted in a wide variety of scientific disciplines, including gerontologysocial psychologyclinical and medical research and happiness economics.

‘Happiness’ is the subject of debate on usage and meaning, and on possible differences in understanding by culture. 

The word is used in several related areas: 

These uses can give different results. For instance the correlation of income levels has been shown to be substantial with life satisfaction measures, but to be far weaker, at least above a certain threshold, with affect measures. 

Source https://en.wikipedia.org/wiki/Happiness