Why does my meta description change all the time on SERPS?

Selected answers from the Dumb SEO Questions Facebook & G+ community.

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  R.Gopi Krishna:  ;
  hello panel hope u r doing good and thanks for clearing my doubts. This time my doubt is on keyword & meta description. When i search for keyword "Famous Places in Italy"i can see my website in first page of google global search result with meta description "Jun 22, 2013 - This section Famous Places in Italy tells about most wonderful ... Rome has got a famous historical architecture “Colosseum” which used to be ..." but if i search for keyword " Things to do in Florence Italy" i can see my website in 5th page of google global search result with meta description "This section Famous Places in Italy tells about most wonderful & desired places in Italy that should not be missed out. It give reader an unique ...” Why is this fluctuation of meta description. Does this mean anything to seo and am I on the right track. ? My webpage is http://www dot touristtiger dot com/famous-places-in-italy/
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  Joseph Paulino: +R.Gopi Krishna ;I did not query your keywords to see this in action, but, I see this happen a lot when Google puts a page in the SERPs and uses the best description to show the page matches the query and so it belongs to the top search results. ;
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  Renu Dhiman: "Famous Places in Italy" is your first keyword that's why its getting a good ranking on Google.  ;But  ;if you would do little seo for the second keyword then it could also get a good rank.