Bounce rate is people telling you "your site sucks"
Bounce rate is the ratio of visits where visitors leave your site from the first page visited. This metric is used to measure visit quality. Page high bounce rate usually means that the page visited isn't relevant to your visitors. The more compelling your page is, the more visitors will click to get more information or convert. You can lower your bounce rates by understanding why your visitors bounce from that page.
in simple terms: Bounce rate measures the number of people who came to your site and didn't click on any link.