If you get Duplicate meta descriptions in htmp improvements section of Google Webmaster tools

Google webmaster tools > Search appearance > Html improvements

Meta description information can give users a clear idea of your site's content and encourage users to click on your site in the search results pages.

Duplicate meta descriptions

You can fix it by deleting site description.

YourElggSite > Administration > Settings > Basic Settings

Delete text in "Short description of your site (optional):" box.