Keyword density

From SEO Wiki

Keyword density is the percentage of words on a web page that match a specified set of keywords. In the context of search engine optimisation keyword density can be used as a factor in determining whether a web page is relevant to a specified keyword or keyword phrase. Due to the ease of managing keyword density, search engines usually implement other measures of relevancy to prevent unscrupulous [webmasters from creating search spam through practices such as keyword stuffing.