Everyone and "registered users"

Hi, what the difference between those types?

I have only one user profile "Registered users" and no one else can see the posts unless a person is registered on the site so he becomes a registered user.
I guess in my case there is no difference but the share button has several sharing options including everyone and registered users. Can some of this options be disabled so it doesn't confuse users? It's just a cosmetic change i think but would be nice to have it. In registered users profile type in the privacy option tab I changed all the settings to "registered users " but it didn't help.

Please advise, thanks