Originally Posted by appkodes

Keyword density tells you how often a search term appears in a text in relation to the total number of words it contains. For example: if a keyword appears three times in a 100 word text the keyword density would be 3%. From the point of view of search engines, a high keyword density is a good indicator of search engine spam. If a keyword appears too often in a website, search engines will downgrade the website and it will then appear lower down in search results.