Google circles are groups of people in the Google+ social platform created to enable easier, more targeted content sharing that are meant to more accurately represent real-life information sharing.
The Circles feature allows a Google+ user to define groups, organize them using drag and drop functionality and then share specific content to specific groups (colleagues, friends, family, etc.), keeping that content hidden from other circles as desired, or allowing circles to overlap. Users can also choose to share with extended circles, which include people in their circles' circles. Google circles have been compared to Facebook groups.
Users can also control the content in their "Stream," where users can see updates from people in their circles, by using a filter that allows no content from a circle, some content, most content, or everything users in that circle publish.
Google circles also help enable direct messaging. Users can start a Hangout with people in their circles, send them a direct message from that person's profile page, or email that person using Gmail without knowing their email address.
Businesses can use Google circles to build their social media presence and boost their brand image by connecting with relevant influencers and potential customers, tracking hot topics of discussion, creating and sharing Google Hangout broadcasts, and more. In addition, having Google+ followers and having people "+1" your content improves Google search engine ranking.