Clemmy sent in: What is the difference between Gmail Groups & Circles?
Both are for grouping related contacts but Groups are for Gmail, where as Circles are for Google Plus. Groups and Circles can have similar names.
In Gmail you may wish create a group for friends, or clients to send a single message to the entire group. You can add your individual contacts to the group, to a circle or both.
Adding people to your Circles, means you want to socially following them, and you will see their public posts in your Google Plus stream. Adding your email contacts to circles within Gmail makes expanding your social circle convenient.