Sgt_Kickaxe - 7:45 pm on Nov 7, 2010 (gmt 0)
The closest I could find on Google to an official description was from this page - [code.google.com...]
Bounce rate is referred to as a single-page visit to your site, but is strictly defined as a single interaction request during a user session. For this reason, a bounce rate for a page is also affected by ecommerce transactions and event tracking requests. This is because these features co-exist with page tracking and, when they are triggered, they result in additional interaction requests to the Analytics servers.
It might be described elsewhere but I haven't found it if it is. It's interesting that Anaytics is mentioned since *I believe* data is gathered from visitors via Google tool bar and not just by your page loading analytics (which you may not even have).