生き甲斐 (ikigai), raison d’etre, reason to live.
I like this Euler diagram because it elucidates different types of “lack” that we might feel in what we do every day. My peers who work in the technology, finance, and professional services industries tend to speak of having “Satisfaction, but feeling of uselessness” or “Comfortable, but feeling of emptiness.” Musician friends speak of “Delight and fullness, but no wealth.”