Google has started to verify a small number of accounts on Google +, such as celebrities, high profile accounts and users that have been added to large number of circles. The Verified badge will appear at the top of the page next to the name in a grey colour.
The announcement was made on Friday evening by Wen-Ai Yu from Google along with a video below. There is no clear definition of how users circles you need to be in to get verified. This is still in its early stages, but i guess over the coming months more user profiles will get verified, and we will have a clear understanding of the verification badge exactly works.