Because after the search query, the search engine cannot make any additional question to the searcher, it must trust on the on-page and off-page information it has. So how on earth the search engine can determine the relevancy, when there are millions of pages available.

Okay, the answer is clear: they must have rules in their memories, which they use. These rules are called algorithm and no-one really knows how they work, because it is a strictly kept business secret. If we internet business entrepreneurs would know them, the Net would be totally different. However we know that all the big search engines follow certain common rules.

1.The Location And Frequency Of The Keyword On An Internet Business Web Page.

This is one of the main rules in the ranking algorithm, a location/frequency method. This means that pages with the search term in the HTML title tag are often thought to be more relevant than others to the topic.

Then the search engines will watch if the search keyword is located in the top of the page, like in the headline or on the first paragraph of the copy, because they think that the relevant keywords are placed right in the beginning.

Then search engines watch the frequency of the search keywords, because they determine the relevancy out of that. So they calculate what is the share of keywords out of all words on the page, this is called the keyword density. The higher the density compared the other words, the more important the term is. However, the density is recommended to be around 4 %, but still the webmaster should reach bigger keyword density than the competing sites.

We know that all major search engines follow this location/frequency method, but they add some customized incredients into it, which no internet business entrepreneur knows exactly. That is the reason, why the same search, internet business, gives so different results in different search engines.

One reason for this is that some search engines do not index all pages but some do. Some index pages more often than the other ones, which leads to the situation that all search engines have a different collection of pages in use, which gives different search results.

Then there is the rejection issue: search engines reject pages because of keyword spamming, too many keywords, which leads to the situation, when pages will be excluded from the index.

2. Off-Page Factors.

Because of some artificial tricks to get better ranking, search engines also look at the off-page factors, when determining the ranking. The key here is the number and the quality of backlinks. The search engine see the backlinks, i.e. links from other sites to your web site, like votes. This means that if the site has lots of backlinks it is seen to be popular and useful for the other sites. Now they can determine, whether the site deserves higher page rank. They also have techniques to judge if the webmaster has used artificial tricks to be able to increase the number of the backlinks.

By the clickthrough counting the search engines measure which of the search results links get most of the clicks. This means that also the result page copy has meaning, because if the searcher will not click the top page, something is wrong and the lower ranked site will get a boost.