Number of visitor who enter site and exit without enter in site other page and leave in specific time out divided by total no. of visitor enter site that page... A= bounce rate, B= total no. of visitors viewing only one page, c= total no. of entries at that page.. (A=B/C)
According to Google, the Bounces field identifies the number of single-page visits to your site over the selected dimension. Visitors who arrived to your page and clicked the back button. Bounce rates indicate that visitors who found your website by searching Google for Keyword 'Z', did not find your website useful and thus went back to search. To Google this is a signal that your site may not be relevant to keyword 'Z' and it may lower your rankings for this keyword. Exits - this metric identifies the number of exits from your site, and, as with entrances, it will always be equal to the number of visits when applied over your entire website. Use this metric in combination with particular content pages in order to determine the number of times that particular page was the last one viewed by visitors. I hope this helps to clarify your doubts.