Search spam (spamdexing) is one of the key concepts of the black promotion of a site, it is the creation of sites or separate pages in order to manipulate search results and deceive the user.
Spam in meta tags
Use of non-content related queries in page meta tags. This type of spam appeared one of the first when search engines analyzed only meta tags. Now search engines index the entire text of the site, while checking the compliance of the specified meta tags with the content of the page.
The use of “invisible text”, text invisible to visitors, but indexed by search engines. The color of the text matching the background color, the text is 1 pixel in size, the text block with the “display: none” style containing a set of key phrases significantly increases the weight of the keyword and thereby makes the page more relevant for this request.
Link spam – links that promote the popularity and pagerank of a site. When building relevant search engines, search engines take into account the number of external links to the site, which allows using artificial methods of link building to promote the site in the TOP:
creating satellite sites on free hosting, registering them in thematic directories and placing links to the main site on them.
the same links from blogs, wikis, etc.
Search engines are struggling with this by creating filters that add sites whose links are not taken into account when ranking.