When you share a link of your post form your website or your blog on facebook it would display the first few lines of the post and use it as content description. This is done by sharing a post using a Facebook share button and also you can Copy The Post link and Past on Facebook.
There are some more option of getting the information form your post are:
First it looks for a description meta tag, and uses the content as description.
If there is no description meta tag in your page then Its looks for the first <p>(paragraph).
Facebook scrapes your page every 24 hours to ensure the description (and other share data) are up to date. However, you can manually refresh it by entering the post URL into the Facebook URL Linter. Click hare to open the Facebook URL Linker Page.
When you open Above link Enter The Link Address of your page in URL Box. (Show in Image Below)
Click on Debug Button.
Facbook Display the Scarp Information . if Its correct then ok other wise click on Fetch New Scrap Button.
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