To see where we are going, let's get back to the basics:
What is Keyword Density?
This is the percentage of times a keyword or key-phrase is found in your content along with the other content on the page.
The formula for this is: ( # of keyword repetition / total words on page)*100
If you want to rank highly for specific pages you have to make sure you don't over stuff your content with your keywords or you might be penalized for trying to manipulate the search engine. That's not to say keyword density doesn't matter. If you keep your keyword density to at least 5%(which I call the sweet spot) along with other ranking factors, this will help boost your page's rank in search engines.
Just a quick question, one of my readers asked me. Hope this helps! :)