As of September 2012, it has a total of 400 million registered users of whom 100 million are active on a monthly basis.
Unlike other conventional social networks which are generally accessed through a single website, Google has described Google+ as a "social layer" consisting of not just a single site, but rather an overarching "layer" which covers many of its online properties.
Google+ originally launched as Google Circles, a name alluding to its emphasis on organising friendship information.
The service was launched as an invitation-only "field test" in June 2011.
Early invites were soon suspended due to an "insane demand" for new accounts.
On September 20, 2011, Google+ was opened to everyone 18 years of age or older without the need for an invitation. It was opened for a younger age group (13+ years old in US and most countries, 14+ in South Korea and Spain, 16+ in Netherlands) on January 26, 2012.
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