I don't think there's an accurate English word for it. In (anglicised) Greek it's called eudemonia and it's an idea that has been proposed by many of the great Greek philosophers.

My definition of it is derived from Aristotle's philosophy on the matter, which I'll very briefly restate (forgive me any inaccuracies, I'm neither fluent in Ancient Greek nor have I learned about that stuff in English):

• every activity serves a purpose / has an aim (purpose and aim will be used interchangeably)

• from the perspective of the person engaging in said activity, that purpose is good

• these purposes have a hierarchical order (ex. below)

• we pursue the lower aims in order to fulfill the higher ones

• there must be one highest aim, which we pursue all the other ones for; otherwise, striving for anything would be as endless as it were pointless

• the highest aim/purpose/good thus must be pursued for its own sake

• this highest good can only be eudemonia

So what is eudemonia? The modern English words that come closest to it are "a constant state happiness" (a mode of being rather than something you experience temporarily; internally generated and not triggered by external stimuli) or welfare (again, it's about the feeling that you've arrived, that everything fits in, not that external influences like what you can afford or not). The term "human flourishing" has been suggested as a translation and in other words, there is an exact translation, so the concept is not as vague as it seems.

Every once in a while I get that feeling that everything has fallen into place, that things are just as I'd like them to be. It doesn't mean I have everything I want, but for the moment, I'm content with the way things develop. If I can have that in a hypothetical endless state - then I have eudemonia.

I promised an example, so here's one all of us should be able to relate to:

In school, you pay(ed) attention (I know we didn't, but let's assume we did for the sake of the train of thought, okay?).

So. In school, you pay(ed) attention to the class (lower activity) in order to geed a got grade (lower aim). You want(ed) to have good grades in order to be able to pursue our dream careers later (intermediate aim). These, you want(ed) to pursue to provide financial stability and / or find a fulfilling job (high aims). And all of these were pursued so you can be happy (-> attai eudemonia) somewhere later in time.