A bounce occurs when a user has just a single-page session on a site and leaves without visiting any of the other pages. The bounce rate, which is sometimes referred to as the exit rate, is the percentage of users who bounce:
As you would expect, as page load times increase, so too does the bounce rate. Examples of actions that result in a bounce include the user closing the browser window/tab, clicking on a link to visit a different site, clicking the back button to leave the site, navigating to a different site by typing in a new URL or using a voice command, or having a session timeout occur.