"Bounce rate is the percentage of single-page visits or visits in which the person left your site from the entrance (landing) page"
This may not be a proper metric. What if the landing page has only external links? The page may be exactly what the user is looking for.
"Use this metric to measure visit quality - a high bounce rate generally indicates that site entrance pages aren't relevant to your visitors"
Google looks down upon this. For example, a page may have a listing of popular DVDs with external links. The user may be looking for a DVD, find it, and click on the external link. This hurts the rankings. I may make a "learn more..." link that goes to a page all about that item and then the user can purchase it. This would be two page views and it would not constitute as a "bounce".