Spamdexing (also known as search engine spam, search engine poisoning, black-hat search engine optimization, search spam or web spam) is the deliberate manipulation of search engine indexes. It involves a number of methods, such as link building and repeating unrelated phrases, to manipulate the relevance or prominence of resources indexed, in a manner inconsistent with the purpose of the indexing system.

Spamdexing could be considered to be a part of search engine optimization, although there are many search engine optimization methods that improve the quality and appearance of the content of web sites and serve content useful to many users.