Meta tags is a hidden text on your web page code that describes what the page is about. Meta tags should contain the keywords that you want to optimize a page for and is used to help crawlers index your page based on the meta tags content. The meta tags descriptions are not visible to the search engine user.
How it works is that search engine crawlers are indexing pages based on their content so that when an online user is searching for something they can match up the search terms with the most relevant pages in their index based on content. That is why it is important for your online marketing campaign that you include meta tags description in the code of your web pages. One important thing to know is that when creating meta tags for your search engine marketing campaign be careful to not use too many keywords as crawlers can index your page as spam. Meta tags can also be used to describe your video content if you are trying to rank it high for effective online video marketing.
To read more go to: http://www.helium.com/items/1915666-an-overview-on-metatag-seo-best-practices