What do you mean by " people talking about this on facebook "

People Talking About This : It is the number of users who have created a “story” about a page in a seven-day period. On Facebook, stories are items that display in News Feed. Users create stories when they:

• like a page
• post on the page wall
• like a post
• comment on a post
• share a post
• answer a question

Basically it shows user engagement on page.

• they clicked on the like
• they made a comment
• they shared an update on their Page or Profile

People talking about this around 8-9% is considered a good performance for a page.