I found a webpage without a `meta`-`description` in the page source but when I did a `site:` search, the webpage had a description. 

How does this play into SEO?

Was the description generated based on a default description possible? If the `meta`-`description` isn't defined in the source under the meta data but there is still one on a `site:` search does Google penalize that page for not having a defined `meta`-`description` in the source?

This website has 210 webpages and only about 15 of them have a `meta`-`description` in the code but using a [`meta`-`description` checker][1] I have found there to be no `meta`-`description` despite one appearing on a `site:` search. 

Of the pages with no `meta`-`description`, they all have the same one that appears on the `site:` search. 


  [1]: http://www.seoreviewtools.com/bulk-meta-description-checker/