Search Engine Optimisation is the use of search engines to draw traffic to a web site. It is the search engine optimisation techniques of attaining a higher ranking in search engines and directories via changes to a site to make it more search engine compatible.
Mainly, it deals with spider-based search engines (i.e. those that find, read and index your site automatically). However, if your site is content-rich and well optimised, it will also gain a lot more weight when a human editor browses your resource and ranks it appropriately for a directory. With the directories, it is as important as with the spider-based engines that your site is error-free, your content is relevant, and your link popularity is considerable.
Search Engine Optimisation is important as it helps you get traffic for free. You may discover that you can obtain the same or even more visitors by optimisation alone, without having to pay for advertising. Many Web surfers tend to ignore paid (sponsored) results displayed by the search engines, yet if your site appears on the top of the first page of SE results for their query, you are almost certain to turn those searchers into visitors.
The Integrated Approach to SEM involves both promotion and maintenance goals. By on-the-page and off-the-page optimisation you achieve good rankings and increase traffic flow. By regular keyword research, traffic analysis and page adjustment you achieve high conversion rate, thus achieving the full potential of your Web site. The technical maintenance and troubleshooting helps keep your site trouble-free, enhancing your visitor's experience and improving search engine spider compatibility. Website maintenance, while of course an important task, is secondary to the primary search engine marketing goals of promotion and traffic analysis