When using Google+, you can start a Hangout at any time. This will begin a multi-person video chat with your circles or the individuals of your choice. Hangout supports up to 10 people in a room at the same. They’re a fun way to hang out with friends and family when you’re online.
Update August 2014: Hangouts has been elevated into Google’s enterprise apps suite. This means that business users are no longer required to have a Google+ account to use Hangouts. To make video calls on Hangouts, users only need to have a Google Apps customer account.