Search engine optimization (SEO) is the process of improving the visibility of a websites

 Getting indexed

The leading search engines, such as Google, Bing and Yahoo!, use crawlers to find pages for their algorithmic search results. Pages that are linked from other search engine indexed pages do not need to be submitted because they are found automatically. Some search engines, notably Yahoo!, operate a paid submission service that guarantee crawling for either a set fee or cost per click.[29] Such programs usually guarantee inclusion in the database, but do not guarantee specific ranking within the search results.[dead link][30] Two major directories, the Yahoo Directory and the Open Directory Projectboth require manual submission and human editorial review.[31] Google offers Google Webmaster Tools, for which an XML Sitemap feed can be created and submitted for free to ensure that all pages are found, especially pages that aren't discoverable by automatically following links.[32]
Search engine crawlers may look at a number of different factors when crawling a site. Not every page is indexed by the search engines. Distance of pages from the root directory of a site may also be a factor in whether or not pages get crawled.[33] Additionally, search engines sometimes have problems with crawling sites with certain kinds of graphic content, flash files, portable document format files, and dynamic content