A search engine is really a huge database of web content. Indexing is the way in which that database is accessed to retrieve content. It is the principle objective of a search engine to match a query made by a person with the right web content. The quality of a search engine’s indexing directly affects the quality of the end-user experience.
Search engines use sophisticated, proprietary mathematical algorithms to index the web content that their respective search engine bots access and scan across the WorldWideWeb. Although it is not possible to know the algorithms exactly, it is the task of the search engine optimization specialist to continually examine historical indexing in order to infer what is required of a web page to be accurately indexed and delivered in the top listing positions of the search engine results pages.
Indexing is the principle function of the search engines and therefore of primary interest in search engine optimization.