Keywords are words that describe your site.
Keywords have to be carefully chosen to represent your site. No longer can web designers depend on metadata to describe the site. Search Engines have become sophisticated enough to go beyond metadata, but no one really knows exactly what the algorithms are for searches.
It’s believed that linking is favored by search engines more than anything else. If other people like your site enough to directly reference it using a hyperlink, that has credibility, and you move up in the search result rankings.
Besides inbound links, the search engines “crawl†through the website looking for what the site is about so it knows how to index it. If you choose your keywords carefully, you can attract your desired readers. Just make sure that the titles you use (page or otherwise) contain the keywords you desire. Same goes for URLs, so think twice before you name your next HTML page.