The meta keyword tag allows you to list the keywords for the page; however, most search engines do not support this tag.
Of the major search engines: Inktomi and Teoma are the few that even take this tag into consideration.
Many people think meta tags are the magic solution to ranking well. Create the perfect combination with the perfect keyword density and presto! Well, that is far from being true - there is more to SEO than good meta tags and there are also many off-page factors. However, it does help to have highly optimized Meta tags.
Meta tags are parts of an HTML document that are used for you to describe the page content for search engines. Meta tags are placed within the head area of an HTML file and with the exception of the Title tag; your visitors do not see them as part of the viewable area of the page.
Sitemaps are an easy way for webmasters to inform search engines about pages on their sites that are available for crawling. In its simplest form, a Sitemap is an XML file that lists URLs for a site along with additional metadata about each URL (when it was last updated, how often it usually changes, and how important it is, relative to other URLs in the site) so that search engines can more intelligently crawl the site.
The Google algorithm's most important feature is arguably the PageRank system, a patented automated process that determines where each search result appears on Google's search engine return page. Most users tend to concentrate on the first few search results, so getting a spot at the top of the list usually means more user traffic. So how does Google determine search results standings? Many people have taken a stab at figuring out the exact formula, but Google keeps the official algorithm a secret. What we do know is this:
Finding useful information on the World Wide Web is something many of us take for granted. According to the Internet research firm Netcraft, there are nearly 150,000,000 active Web sites on the Internet today. The task of sifting through all those sites to find helpful information is monumental. That's why search engines use complex algorithms -- mathematical instructions that tell computers how to complete assigned tasks.
Google's algorithm does the work for you by searching out Web pages that contain the keywords you used to search, then assigning a rank to each page based several factors, including how many times the keywords appear on the page. Higher ranked pages appear further up in Google algorithm search engine results page (SERP), meaning that the best links relating to your search query are theoretically the first ones Google lists.
For Web page administrators, being listed prominently on Google can result in a big boost in site traffic and visibility. In 2007, Google surpassed Microsoft as the most visited site on the Web. With that much traffic, getting a good spot on a Google SERP could mean a huge boost in the number of site visitors.