I'm guessing it has something to do with how quickly the user returned back to the search results. For example, you're searching for something specific and clic

I'm guessing it has something to do with how quickly the user returned back to the search results. For example, you're searching for something specific and click on the #1 result. If you visit site #1, go back to the results, click on #2 then visits to #1 could be seen as a "bounce". Of course this could theoretically be gamed, but that's for another discussion.