These tags are part of the HTML code. A Web author may surround sentences, even whole paragraphs, with these tags. Certain spiders then read the information in the tags as a way to help them index the site. After you have done all the right things with text, keywords, Meta tags, etc. submit yourself to the following search engines. Strange things happen.
Pages disappear from catalogs.
Links degrade . Watch for trouble, and resubmit if you spot it. The engines have grown smart enough to realize some sites only change content once or twice a year, so they don't visit regularly. Resubmitting every month or two will ensure that your site's content is kept current. Some search engines take weeks or months before they update their catalogs.