[Drolefille]

Flagship chapter is usually one held up as a leader or example. For example I found a Pike newsletter that described their Beta Mu chapter as "the flagship chapter of the southwest." Whether it's an official designation in an organization or not, it means you win awards, are a strong chapter, have high GPAs, all the things that your org cares about.

I don't usually see it used for NPCs, but NPHCs and NICs tend to use it a lot.