Who can tell me the rules that description tag in Google result.

Hello,I am a new man in webmaster.and I have a question about descriptions display in Google Search result. I display my screenshot here.



As the picture show,one of the result's description show its page information.
But the other show its description tag.
who can tell me why?

 

post big image nothing view-able in this image.

 

this picture is right!

 

I agree with chasen, actually the description tag describes the brief information (clubed in 155 character, as per google guidelines) about the page.

 

when google fetch data from some shopping related sites it is also fetch some data from page because always description tag not have proper data which is already set in the page that is why google fetch page information when ever he required.

 

I still have question to ask: when google think page don't have proper data to fetch.It nessery for us to know and get skills to hand it.