From b2evolution manual

This page only includes hits identified as made by a web browser (as opposed to an indexing robot/spider or an XML feed reader).

• Refering searches: Hits coming from search engines such as Google, Yahoo, Microsoft Live, Ask or more.
• Referers: Hits coming from other sites linking to your blog.
• Direct accesses: Hits from people who typed in your URL or have it bookmarked.
• Self referred: Hits from people who are following an internal link on your site/blog.
• Special referers: Hits from webmails, caches, redirectors, etc.
• Referer spam: Hits coming from sites identified as spam in your blacklist.
• Admin: Hits within the Admin interface (also includes previews).