Keyword Stuffing Examples
Keyword stuffing are "Black Hat" techniques. Methods of keyword stuffing include:

Invisible text: which is placing lists of keywords in white text on a white background in hopes of attracting more search engine spiders. Not a good way to attract searchers or search engine crawlers but a good way to get your site banned!

Tiny Text/Alt Text: the placing of keywords and phrases in the tiniest text possible throughout a web site. While most people can't see them, spiders can. Alt text spamming is stuffing the alt text tags for images with unrelated keywords and/or phrases.

Mirror or Duplicate Sites: duplicating a website, renaming it, and submitting it again. Not only is this ill advised, it is just plain absurd. It is a fools errand! Search engines will know! Submitting a website to a search engine or directory repeatedly in a short period of time is an easy way to get your site banned.

Doorway Pages: basically a doorway page is a “fake” page that the user never sees. Doorway pages are simply HTML pages customized to a few specific keywords or phrases, programmed to be visible only by specific search engines and their spiders. The intent of these doorway pages is to trick the search engines into giving these sites higher rankings.

Sounds good, so what’s wrong with that? Well these doorway pages are not static destinations they are targeted towards specific search engine spiders. As a result when a searcher lands on a doorway page, they are instantly redirected to the "actual" website which in most cases is totally unrelated to the users search.
In simple terms, doorway pages is, just bad SEO. Most if not all search engines have guidelines prohibiting the use of doorway pages. Doorway pages are considered "spammy". While such SEO practices might work in the short-term eventually they will result in your site being flagged and censured.

Take heed! Keyword stuffing will result in your site being penalized by search engines.

Search Engines Definition of Spam.
Basically spam, as it applies to SEO refers to any unethical practice used for the specific purpose of tricking search engines into increasing a websites ranking. Below is a summary of what Google, Yahoo, MSN and Ask consider to be spam:

Google defines spam as; "trying to deceive (spam) our web crawler by means of hidden text, deceptive cloaking or doorway pages." You can report suspected sites at Google's page.
Yahoo defines spam as; "pages (that) are created deliberately to trick the search engine into offering inappropriate, redundant or poor-quality search results." They have an extensive list of what techniques they consider spam at their Yahoo Search Technology Content Quality Guidelines page.
MSN Search; has listed a few spamming techniques "discouraged" by MSN Search; among them are keyword stuffing, invisible text, or false links.
Ask defines spam as; "the practice of purposely deceiving a search engine into returning a result that is unrelated to a user’s query, or that is ranked artificially high in the result set." They too have quite a few examples of search engine spam.

This is not a list of all search engines, but it will give you a good idea of what search engines consider to be spam.

Black Hat Consequences.
The use of these unethical (black hat) tactics designed for the specific purpose of tricking the search engines may generate short-term results but eventually will come back to haunt you. You could reap a whirlwind! Search engines are ingenious, they know people are trying to trick them to get higher rankings. Consequently they are constantly changing their algorithms.

If your website is doing something that is considered black hat or even in the gray area, do yourself a favor. Fix it! If an SEO company you are considering is proposing to use any of these tactics, run don't walk away from them. and find someone who can truly help your business in the long run.

We can help you achieve your business goals. We are a “white hat” SEO business. We do not use gimmicks or unscrupulous (black hat) search engine techniques. While Black Hat SEO may sometimes achieve results, they will often be short lived and could get your site removed and "blacklisted" from search engines. Rather we adhere to search engine's best practices and perform legitimate code optimization, optimized copy writing and editing that meets search engine rules and makes for top search engine positioning that lasts and continues to perform well for months and, in many cases, years.