Here's how the audiences are defined:
Direct
When a reader navigates to a site by typing in the url into the address bar.
Social
When a reader navigates from one of these sites:
- Google+
- Me2day
Search
When a reader navigates from one of these sites:
- Bing
- Yahoo
- Baidu
- Yandex
- Naver
- Daum
- Nate
Email
When a reader navigates from an email campaign. Note that this is not always guaranteed to be successfully detected.
Other
If there is no referer present, or if there is a referer, but it's unrecognized by any of the categories above.