Bounce is visit in which the user left your site from the landing page without visiting other pages of your site so Bounce rate is the percentage of single-page visits.
If bounce rate is high this may suggests that the site content may not be relevant to what the user/visitor is looking for or may be all the content is provided on a single page.
There could be number of reasons which can lead to a high bounce rate.
(a) There may be poor site design or usability issues.
(b) The content may not be relevent.
(c) Site may take long time to load.
(d) Tracking code may not be installed on all your pages.
(e)Site may not be optimized for mobile viewers i.e. visitors viewing your site leave promptly after landing on entrance page.
(f) Also if Bounce rate is very high, remember to check your referral traffic just in case if there is spam referral traffic which is inflating your Bounce rate. For example traffic in the following screenshot from referral site such as get-free-social-traffic.com or snip.to are all spam & irrelevant and have 100% bounce rate.
(g)Flash Based Sites
If sites use Flash or other interactive technologies, these kinds of sites don’t load new pages frequently and generally all user interaction takes place on a single page. i.e. for such sites it is common to have high bounce rates & nothing to worry about.
Solution: Explain your webmaster to work on above areas such as setting up filters to remove spam referral traffic, to make your website optimized for mobile, verify that GA code is installed on all your website pages and your site loading time to be optimized, check user behavior and identify if there are any usability issue, etc.
Should there be any other query you are welcome to leave your feedback.