With certain html code it is possible to emphasize text both for visitors and search engines.
Some text is not directly visible for visitors like the text that is included within the description metatags. If relevant to the search term this may be displayed on the search engine result pages.
Other metatags like the keywords metatag are never displayed for the visitors benefit, but are still used by search engines to establish the relevancy of a page to a search term.
This webinar is a live seminar showing how to use HTML emphasis.