If the results were not what people were looking for the Search Engines would loose credibility and they would use another one. So Search engines use a number of different ways to see what the website and more specifically the web page is about. They use the webpage it self and all that is contained in the webpage. People are not usually exposed to the meta data. There are things like H1 and H2 tags that tell the importance of certain words. Search engines use these markings for knowing the subject matter of the page.
Search engines also use metrics such as how long visitors stay on the site and page. They use social signals that tell the search engines that people find pages valuable.
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