I’ve just recently been thinking about this, specifically about our lack of agreement on what is meant by happiness.
My understanding is that happiness transcends momentary fluctuations in mood. It’s an underlying OK-ness that’s unperturbed by transient brain chemistry phenomena. Episodes of anger, sadness, fear, bliss, passion, etc. are just surface ripples on this deep ocean of OK-ness.
I think it’s easy to get caught up in the surface fluctuations, so that we’re always chasing after the moments of bliss and desperately trying to fend away the moments of sadness. But I think happiness is the skill of not getting sucked into that chasing and fleeing game, but just letting those states be, knowing that OK-ness is your fundamental condition.