Google's generation of page titles and descriptions (or "snippets") is completely automated and takes into account both the content of a page as well as references to it that appear on the web. The goal of the snippet and title is to best represent and describe each result and explain how it relates to the user's query.
How snippets are created
Snippets are automatically created from page content. Snippets are designed to emphasize and preview the page content that best relates to a user's specific search: this means that a page might show different snippets for different searches.
... ie the description you see in search results, is a 'generated' snippet. It is NOT the 'meta description'