I like the analogy between G+ circles and friendship. A person can become your friend if he is in more than one your circle. Let's say you have a circle called

I like the analogy between G+ circles and friendship. A person can become your friend if he is in more than one your circle. Let's say you have a circle called "work" and you invite somebody from it to play football together. If he accepts, the transition happens. A person that you work with is a coworker, a person that you play football regularly with is just a teammate, but combined they become a friend.