Google Buzz makes Gmail social by letting users view media and status updates shared online by their friends. This format is popular with Facebook and Twitter. Status update through Buzz is not limited to 140 characters.
From Google Blog: Our belief is that organizing the social information on the web — finding relevance in the noise — has become a large-scale challenge, one that Google’s experience in organizing information can help solve. We’ve recently launched innovations like real-time search and Social Search, and today we’re taking another big step with the introduction of a new product, Google Buzz.