- The number of times unique users returned to your website in a given time period
- The percentage of visits when a user landed on your website and exited without any interactions
- The percentage of total site exits
- The percentage of sessions in which a user exits from your homepage
A bounce is a single-page session on your site. In Analytics, a bounce is calculated specifically as a session that triggers only a single request to the Analytics server, such as when a user opens a single page on your site and then exits without triggering any other requests to the Analytics server during that session.
Learn more here: https://support.google.com/analytics/answer/1009409