Keyword Density refers to the number of times your keyword is repeated on the given web page. Keyword you are targeting need to be there in the web page with minimum keyword density.
Keyword density is that search engines use this information to categorize a site's theme and to determine which terms the site is relevant to. The perfect keyword density will help achieve higher search engine positions. Keyword density needs to be balanced correctly.My advice that try to include your keywords without worrying about the 3 to 4% keyword density.
keyword density is the measurement in percentage of the number of times a particular keyword or phrase appears compared to the total number of words in a page.