It's the Google Play store, but on your Nook HD/HD+ only the apps that work on the HD/HD+ will show up. I believe some apps won't show up because the app developer says the app 'needs' gps, which the HD/HD+ does not have.
I believe they can change a setting in the app that would make it available for the HD/HD+, but you would need to contact the app developer, not B&N.
If I'm wrong on any of this someone please correct me.
Thanks, sygram. Makes sense to me.