Keyword density refers to the keyword distribution of the page. You should be careful about it if you want a good result. We cannot put too many keywords at one place wishing it will give you good search engine result.
The keyword density help webmasters and SEOs to achieve their optimum keyword density for a set of key terms.Keyword density is important because search engines use this information to categorize a site's theme, and to determine which terms the site is relevant to.
Keyword density is the percentage of times a keyword appears in the web page compared to the total number of words on the page. In the context of search engine optimization keyword density can be used as a factor in determining whether a web page is relevant to a specified keyword or keyword phrase. 2% to 3% keyword density is good for seo
Keyword density, as far as how it relates to good SERPs, is a myth. A keyword / phrase only needs to be on a page once. You will not get penalized for putting a phrase on a page too many times. Except you'll get penalized by your customers if a page is written all spammy.
Keyword density is still per cent compared to the rest of the text in the keyword appears in content. In general, this metric is a fairly useless for SEO. I as a script it better than you would focus on other metrics do not bother building. You might find this reference useful.
You've already been given fine definitions of what keyword density is all about, so I wouldn't repeat that again. I just want As with most things in life, balance is the key. You need to find the right balance of keywords compared to the amount of content on your page - too many and your site is likely to be considered spammy.