This question has increasingly been explored in the fields of economics and psychology over the last few years. I certainly think of it often, particularly if I’m meditating on the first of the four Brahmavih?ras—the wish that all sentient beings be happy. What am I wishing them, exactly?

Matthieu Ricard, a French monk in the Tibetan tradition, wrote a wonderful book in which he explores the question at length, very incisively. Below are excerpts from Happiness:A Guide to Developing Life’s Most Important Skill that address the question directly.
There exists a way of being that underlies and suffuses all emotional states, that embraces all the joys and sorrows that come to us. A happiness so deep that, as Georges Bernanos wrote, nothing can change it, like the vast reserve of calm water beneath a storm. The Sanskrit word for this state of being is sukha.
Sukha is the state of lasting well-being that manifests itself when we have freed ourselves of mental blindness and afflictive emotions. It is also the wisdom that allows us to see the world as it is, without veils or distortions. It is, finally, the joy of moving toward inner freedom and the loving-kindess that radiates toward others.
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Although intrinsically different from happiness, pleasure is not its enemy. It all depends on how it is experienced. If it is tainted with grasping and impedes inner freedom, giving rise to avidity and dependence, it is an obstacle to happiness. On the other hand, if it is experienced in the present moment, in a state of inner peace and freedom, pleasure adorns happiness without overshadowing it.
The difference between joy and happiness is more subtle. Genuine happiness radiates outward spontaneously as joy. Inner joy is not necessarily manifested exuberantly, but as a luminous appreciation of the present moment, which can extend itself into the next moment, creating a continuum that one might call joie de vivre. Sukha can also be enhanced by unexpected delights. And yet not all forms of joy proceed from sukha—far from it. As Christophe Andre stresses in his work on the psychology of happiness:”There are unhealthy joys, far removed from the serenity of happiness, such as that of vengeance . . . There is also calm happiness, often far removed from the intrinsic excitation of joy . . . We jump for joy, not happiness.”
We have seen how hard it can be to agree on a definition of happiness and have tried to pin down the meaning of true happiness. The word joy is equally vague, since, as the psychologist Paul Ekman has shown, it is associated with feelings as varied as the pleasures of the five senses: amusement (from the chuckle to the belly laugh); contentment (a calmer kind of satisfaction); excitement (in response to novelty or challenge); relief (following upon another emotion, such as fear, anxiety, and sometimes even pleasure; wonder (before something astonishing and admirable, or that surpasses understanding); ecstacy or bliss (transporting us outside ourselves); exultation (at having accomplished a difficult task or undertaken a daring exploit); radiant pride (when our children earn a special honor); elevation (from having witnessed an act of great kindness, generosity, or compassion); gratitude (the appreciation of a selfless act of which one is the beneficiary); and unhealthy jubilation, schadenfreude (relishing someone else’s suffering, such as through revenge). We might also through in rejoicing (in someone else’s happiness), delight or enchantment (a shining kind of contentment), and spiritual radiance (a serene joy born from deep well-being and benevolence), which is indeed more an enduring state of being than a fleeting emotion.
These emotions all possess an element of joy, generally bring a smile to the face, and are manifested by a specific expression and tone of voice. But in order to participate in or contribute to happiness, they must be free of all negative emotions. When anger or envy interrupts, joy is abruptly extinguished. When attachment, egoism, or pride creeps in, it is slowly smothered.
If joy is to endure and mature serenely–if it is to be, in the words of Corneille, a “blossoming of the heart”–it must be linked to other aspects of true happiness: clarity of mind, loving-kindness, the gradual withering of negative emotions, and the disappearance of selfish whimsy.
It’s an extensive catalogue. Would you add anything?