Exit Rate is the percentage of times a specific page was last in a visit (a visit is the activity of one visitor within a single browser session).
An Exit Page is the last page on a site accessed during a visit, signifying the end of a visit. The visitor who exits might have visited other pages on your site, but just exited on that specific page.
Exit Rate is important for determining which page in a process isn’t performing up to expectations.
Bounce Rate is the percentage of single-page visits.
Bounce Rate is important for determining how your landing pages perform as compared to visitor expectations (which directly affects revenue and ROI).
There are a number of reasons why you might have a high bounce rate. For example, visitors might leave your site from the entrance page in response to site design or usability issues. Or - it might just be that certain pages on your site have a high bounce rate for more concrete reasons, such as single-page sites or direct access through bookmarked pages