Google Plus (Google+) is Google's Social Networking service. I love it. You can create circles (groups of people) and only share things with the circles you choose, can have Hangouts (video conferences), share resources, have conversations, and much more. Google+ doesn't have all the ads and games that Facebook does and has a cleaner layout. I think it's a great resource for educators to use with colleagues and with students. You can share resources, have discussions and learn from colleagues. With students, you can post resources, have a Hangout as a help session, and much more.
I've written about Google+ in education many times:
Google+ - More Reasons its great for Education
Google+ and Google+ Pages - great for educators and schools
10 Ways to Use Google Plus in the Classroom
Teaching with Google Plus - tips and resources
Twitter, Google Plus, Facebook - a nice comparison
Google Plus now open to Teens, with safety features
Here is an infographic with some interesting facts and statistics about Google+
