It is when people come to your site and then bounce away to another site, the rate is measured by countint the number of people that come into your site and leave within a certain time perio to go to another site or back from where they came
The bounce rate represents those who visit only one page on your site. (If you don't configure your web tracking software properly, it will not give you an accurate bounce number) To analyze the bounce rate, any low bounce rate numbers are good. Anything high means that the quality of traffic (or it's relvancy to your site) are not great. In some cases, HTML or design problems can prevent a user from using your site - so it's best to set an alert if you have a high bounce rate.
Bounce rate is the term used for the traffic on your site. It gives the ratio of how many visitor just visited the site from some link and navigated else where or were not interested in the site. This also decides how much good content does your site have. Whether it is able to hold the customers, are user convinced by your site content.