Spamdexing (also known as search spam or search engine spam)[1] involves a number of methods, such as repeating unrelated phrases, to manipulate the relevancy or prominence of resources indexed by a search engine, in a manner inconsistent with the purpose of the indexing system.[2][3] Some consider it to be a part of search engine optimization, though 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.[4] Search engines use a variety of algorithms to determine relevancy ranking. Some of these include determining whether the search term appears in the META keywords tag, others 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, people working for a search-engine organization can quickly block the results-listing from entire websites that use spamdexing, perhaps alerted by user complaints of false matches. The rise of spamdexing in the mid-1990s made the leading search engines of the time less useful.

Is it allowed by Google as optimization method ?

This sound a little sneaky and definitely dark gray hat SEO. I defer to Canada Fred for the final word on this one as he seems to have a good handle on what is black hat.

Any question regarding Google and SEO could be found here:
http://www.google.com/webmasters/doc...rter-guide.pdf.

It's a GreyHat technique. Should the content of webpages be just a mishmash of the content of other webpages then eventually (or perhaps even already) the search engine will realize this and demerit or give merit to webpages as appropriate.

Thanks for making the things clear canafred

Black Hat SEO uses illegal ways just to get back links.. Some of the techniques of black Hat SEO are the following:

1. Cloaking
2. Link-farms
3. Spamming
4. Uses hidden text

Not to dwell on semantics but lets be clear, there are no laws against black hat techniques. There are consequences and penalties but so far there are no laws on the books.

Just found this blog post about Black Hat SEO that does a really good job explaining the whole topic.

http://www.seotrafficspider.com/blackhat.html