Keyword Density is the percentage of occurrence of your keywords to the text in the rest of your webpage. It is important for your main keywords to have the correct keyword density to rank well in Search Engines.
Keyword density is an important part if you write for the web and write SEO articles. keyword density basically indicates the amount of times that a selected keyword or keyword phrase appears on a web page or in an article on said page.
Keywords should be used throughout the article but you do not want to over use them. If you repeat them too often, your article or web site could be misconstrued as attempting to spam search engines or artificially boost your search engine rankings.
The accepted standard for keyword density is between 3% and 5%, so to get recognized by the search engines and you should never exceed it and you would want to have a 3% density at the minimum.
Remember that this rule applies to every page on your site and to every article that you write for the web or your own web site. It also applies to not just to one keyword but also a set of keywords that relates to a different product or service.
How to Check Keyword Density:
For example, imagine that you have 100 words on your web page. Do not include the HMTL code used for writing the web page. Imagine that you use a certain keyword five times on the page or in that article. The keyword density on that page is figured by simply dividing the total number of keywords, by the total number of words that appear on your web page. So five divided by 100 = .05. Because keyword density is defined as the percentage of the total word count on the page, multiply the above by 100, that is 0.05 x 100 = 5%.