I know the difference, but I have found some of the official documentation written by Linden Lab misuses the term Market or Marketplace when they are speaking of the Sansar Store. I suspect this is a symptom of the fact that many of the developers came from working on Second Life.
I would gladly point you to the misused words, but I am concerned that you would consider me a bit too picky. So I remain silent. After all.... we are constantly reminded that Sansar is not SL 2.0. And the Sansar Store is not the marketplace.
Proofreading the material written by Linden Lab is not our place, and a rather basic search for the term Market and Marketplace would surely help you find it.