Spamdexing is the repeated and inappropriate repetition of keywords in the content of a web page. The sheer volume and quantity of the keywords may put the page high on the search results list of search engines. Keywords are usually drawn from keyword generators, but since the content of the site usually matters very little to the optimizer, they are often drawn haphazardly.
The strategy is intended to draw traffic to sites with minimal effort, usually to increase advertising revenue. However, spamdexing is usually frowned upon by search engine companies and web surfers. It often causes people to go to web sites that are not relevant to their searches, leading to unsatisfactory experience. Because of this, spamdexing is considered to be a “black hat” SEO tactic.
Spamdexing may be effective initially; however, it’s not an efficient way to draw traffic to a site in the long run. This is because sites suspected of spamdexing are now flagged by modern search engines, which are advanced enough to detect the tactic. Users that encounter sites that spamdex can also manually report them to the search engine. If a site is found to be using this method, it will be put on a blacklist and removed from search result lists. Thus web site creators are better off using legitimate "white hat" SEO methods, which will increase traffic over time.
For more information on spamdexing, try http://www.associatedcontent.com/article/2692821/what_is_spamdexing.html