It involves several methods, such as link building and repeating unrelated phrases, to manipulate the relevance or prominence of resources indexed in a manner inconsistent with indexing the system.

Spamdexing could be considered to be a part of search engine optimization, although many SEO methods improve the quality and appearance of the content of websites and serve content useful to many users.

Overview

Search engines use a variety of algorithms to determine relevancy ranking. Some of these include determining whether the search term appears in the body text or URL of a web page. Many search engines check for instances of spamdexing and will remove suspect pages from their indexes. Also, search-engine operators can quickly block the results listing from entire websites that use spamdexing, perhaps in response to user complaints of false matches. The rise of spamdexing in the mid-1990s made the leading search engines of the time less useful. Using unethical methods to make websites rank higher in search engine results than they otherwise would is commonly referred to in the SEO (search engine optimization) industry as "black-hat SEO".

These methods are more focused on breaking the search-engine-promotion rules and guidelines. In addition to this, the perpetrators run the risk of their websites being severely penalized by the Google Panda and Google Penguin search results ranking algorithms.

History
The earliest known reference to the term spamdexing is by Eric Convey in his article "Porn sneaks way back on Web", The Boston Herald, May 22, 1996, where he said:

The problem arises when site operators load their Web pages with hundreds of extraneous terms so search engines will list them among legitimate addresses. The process is called "spamdexing," a combination of spamming—the Internet term for sending users unsolicited information—and "indexing."