The Meta tag in html is not a required tag when you're creating your web pages. META tags can be very useful for Web developers though. They can be used to identify the creator of the page, the keywords and description of the page, and the refresh parameter (which can be used to cause the page to reload itself, or to load another page). And these are just a few of the common uses!

The use of MetaTags increases the possibilities that your page will be found in a search engine. The meta tag is used by search engines to allow them to more accurately list your site in their indexes. There are several meta tags, but the most important for search engine indexing are the description and keywords tags. 

The description tag returns a description of the page in place of the summary the search engine would ordinarily create.

The keywords tag provides keywords for the search engine to associate with your page.

Here is how  Meta Tags look:
     <META name="resource-type" content="document"> 
          The only resource type that is currently in use is "document". 

     <META name="description" content="a description of your page"> 
          Depending on the search engine, this will be displayed along with the title of your page in an index. "content" could be a word, sentence or even paragraph to describe your page. Keep this reasonably short, concise and to the point. 

     <META name="keywords" content="a, list, of, keywords"> 
          Choose whatever keywords you think are appropriate, separated by commas. Remember to include synonyms.

There are more MetaTags that you can use. There are even MetaTags that allows you to exclude your page from a search. To find more about this visit:

Web Studio 
Dictionary of HTML Meta Tags