I never heard of this before, but found this on Google.
The Bounce Rate is the percentage of bounced visits to your site.
A bounce is calculated as a single-page view or single-event trigger in a session or visit.
The following situations qualify as bounces:
A user clicks on a link deep into your site sent by a friend, reads the information on the page, and closes the browser.
A user comes to your home page, looks around for a minute or two, and immediately leaves.
A user comes directly to a reference page on your site from a web search, leaves the page available in the browser while completing other tasks in other browser windows and the session times out.
So now you and I both know exactly the same on this subject. I hope you get some good answers to this question.