Keyword Density relates to the number of times a keyword/key phrase appears on a webpage. This, divided by the total number of words that appear on a page, gives you a percentage. The higher the better – but not too high. You don’t want to be penalized for keyword stuffing.
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 as a factor in determining whether a web page is relevant to a specified keyword or keyword phrase.
In the late 1990s, which was the early days of search engines, keyword density was an important factor in how a page was ranked. However, as webmasters discovered this and the implementation of optimum keyword density became widespread, it became a minor factor in the rankings. Search engines began giving priority to other factors that are beyond the direct control of webmasters. Today, the overuse of keywords, a practice called keyword stuffing, will cause a web page to be penalized.
Many SEO experts consider the optimum keyword density to be 1 to 3 percent. Using a keyword more than that could be considered search spam. Search engine optimization where that phrase is used four times and there are four hundred words on the page, the keyword phrase density is (4*3/400)*100 or 3 percent.