metatags provide information about web-sites. They are invisible on the page, and can contain for example a page description that google picks up for showing in the search results. A list of keywords is also commonly added using a meta tag.
Here is an example:
<meta name="description" content="My very cool webpage on pets.">
<meta name="keywords" content="dogs, cats">
<meta name="author" content="John Doe">
