What does bounce rate mean in Google Analytics?
Dr Nili Marcia

The bounce rate of your site is an extremely important thing to monitor. The bounce rate is the rate at which visitors leave or 'bounce off’ your website instead of clicking through to other pages on your website. If a visitor goes to your site and hits the back button, closes down the browser, types in a new URL or clicks to another website, this is called a bounce.

See our article Ways to improve your website's bounce rate for ideas on how you can keep people on the pages of your website for longer.