Google+ has two mechanisms for online identity. One is the user profile and the other is a company/organization page.
They differ in two key ways.
A G+ user profile CAN add (or delete) anyone or any page into a circle to share messages, photos etc. The profile is a single person, the management duties cannot be shared.
A page is a company/organization. It CANNOT add (or delete) anyone unless that person agrees by initially "circling" the page. Management of the page can be shared among any number of people (as might be done by Honda Motors).
Naturally I had to create a Poltrack Family page along with a few others. Facebook has a similar arrangement with groups and pages, so the concept should not be unfamiliar.
How can the Poltrack Family page be useful? Quick answer - common repository for sharing family photos.
However you can also add a new tag with a PAGE name and the PAGE will be notified. Pages are like people (just like corporations). In this way the page manager can display photos from a number of different profiles at a single location. The daily photo theme pages work this way and they have thousands of viewers.
What do you need to do to get circled by a page? You need to circle it first!
Here is a screen shot of Page tag that was added to a photo. My dad's furlough in 1943. On the right I clicked ADD A NEW TAG and entered the page name Poltrack Family. I could have added Honda or Ford but that wouldn't make sense would it?