What is search engine spam, or SEO spam?

Defining Search Spam

In the search engine world, spam is defined as the manipulation of a web page to give it an artificial boost in the search engine rankings. Generally, spam is what the search engines say it is. I.e., it is defined by the search engines themselves. Each of the major search engines provide specific guidelines describing what webmasters should and should not do to their web pages in order to achieve a better search engine ranking, though that has not always been the case.

Several methods are universally deemed search spam, including hidden text, doorway pages, and mirror pages.