Direct from Official Google Buzz Blog

Google Buzz - new start to social networking

Google Buzz is a new way to start conversations about the things you find interesting. It's built right into Gmail, so you don't have to peck out an entirely new set of friends from scratch — it just works. If you think about it, there's always been a big social network underlying Gmail.

Google Buzz - an easy-to-use sharing experience

Buzz brings this network to the surface by automatically setting you up to follow the people you email and chat with the most. We focused on building an easy-to-use sharing experience that richly integrates photos, videos and links, and makes it easy to share publicly or privately (so you don't have to use different tools to share with different audiences).

Plus, Buzz integrates tightly with your existing Gmail inbox, so you're sure to see the stuff that matters most as it happens in real time.