What is Keyword Density?

Keyword density (SEO) is the percentage  (%) of times a keyword or key phrase appears on a web page in comparison with the total number of words on the page.

You may want to check these two articles for more information:

http://www.microsystools.com/products/keyword-research/help/website-seo-page-content/

http://www.microsystools.com/products/keyword-research/help/keyword-density-analyzer-tutorial/

Keyword density is the percentage of times a keyword or phrase appears on a web page compared to the total number of words on the page. In the context of search engine optimization, keyword density can be used to determine whether a web page is relevant to a specified keyword or keyword phrase.

Keyword density is the percentage of times a keyword or key phrase appears on a single web page compared to the total number of words on that page.

Keyword density is the percentage of times a keyword or keyword phrase is found in your page content amidst all the other content. For example, if you have a Web page with exactly 100 words on it, including all headlines, captions, alt text, and advertising, and you have a keyword phrase that is on the page 3 times, your keyword density is 3%:

For for more information + an easy way to check weighted keyword density see this: https://www.microsystools.com/products/keyword-research/help/keyword-density-analyzer-tutorial/ (where "weighted" means keywords in title and headers hold more value when calculating the total keyword density scores)

Keyword density let you know how many time you have used the particular keyword or keyword phrase in web page.