What @WendyGoh was saying was Private in a more loose sense. As in, it is private if you don't advertise it. There is no way to make it fully private from our end.
The OAuth url is key to the kingdom here. Without it, it cannot be installed on a portal. Hope that helps.
That actually does clear it up, thanks. I was beyond fustrated with a number of things when I made that post, so my apologies if it came through.
Is it advisable, or useful in any way, to do something like an odd naming convention to help hide/shield the app from users searching in the marketplace?
I understand that no one can connect, I'm just wondering how invisible I can make the app.
There is one point of confusion that maybe it is just me at the end of the day and my brain stopped working, but why would you put it in the marketplace at all? I have several apps in my account that I use for testing things and none of them are in the marketplace. I just used the OAuth url to connect my personal portal to the apps and when it went through the verification, it works as expected.