Search engines operate by using a program called a ‘robot’ or a ’spider’ to find web pages and catalog them in a database. When the spider catalogs your site, it reads and stores everything that is in the source file, not just the part that the user sees. This means it scans and stores all the information in the head and the body of the web page.
Once the search engine catalogs your page, it is available in the search engine’s index. Users can then search this index by performing ‘queries’ in the search engine. A search engine query is simply a search. A typical search consists of one or more words grouped together. The more words a user types in, the more refined or specific the search engine’s results will be.
Once the user performs the search, the search engine returns a results page showing all the pages in its index that it considers a match for the search terms. The search engine will rank the results by relevancy, providing the most relevant results at the top of the list. The search engine will find all the documents containing the words the user searched for and return them in a list to the user. The search engine determines which documents are the most relevant by counting the number of times the words appear together within the document. Additional factors considered include the placement of the keywords within the document.
Every search engine has unique and complex methods, called algorithms, for determining relevancy. Although parts of the methods search engines use are known, complete information is hard, if not impossible, to come by because none of the search engines make their methods for determining relevancy public. Ranking methods are also known to change frequently in order to help the search engines better determine relevancy but also to make it harder for people to manipulate the rankings.
Knowing what factors search engines use to rank web pages and then manipulating those factors on your web pages is what search engine optimization is about.
