Creating links from other relevant websites to yours to improve your link popularity and therefore improving of your ranking with many of the search engines. Estimates are that only 2-5% of the websites today have been optimized. With the growing number of websites being added by businesses and individuals, the only way to stay visible in the World Wide Web is SEO. Optimization helps your site to obtain top rankings. Website optimization is not cheap, it requires many hours of analysis and investigation by experts. But the results can be astounding. Your website visibility can increase dramatically, saving you a lot of money that you would constantly need to spend on advertising otherwise.
Remember SEO is not using trickery to fool the search engines. It is not using spamming techniques that will only improve your chances of being dropped from search results altogether. It does not involve the use of "throwaway" domains or "shadow" domains. Such tricks will cause you to be dropped completely and at best only work for a short time.