Keyword Density is a term that some of us SEO experts use to describe how many times each specific keyword shows up on a specific page of your website. Search engines check this to make sure you are not over-saturating your keywords. In other words, search engines want to know if you are spamming or not.

As I mention often in my SEO Guide and in the SEO FAQ, you want the most original, helpful and honest content possible in order to be taken seriously by both search engines and potential visitors. If you are spamming keywords, chances are both the search engines and your visitors will know it. A good rule to remember is to keep your keyword density for each keyword below 5% of the page's content. If it truly is a keyword that you want to emphasize, your best bet is to keep the density between 2% and 4%. This gives you a safe margin on either side - you don't want to overemphasize it and make it look like you are spamming keywords - but you also want to mention it enough times so that it is obvious to search engines what your page is about.

You can easily do this using natural sounding language. You'll notice that you'll be pretty close to this density range when you arn't even thinking about it. You can go back and check your percentages to make sure that you are not too low or too high in density, but for the most part, if you are writing about a subject that has to do with your main keyword(s) in normal, natural sounding language, chances are you won't have to do much editing.

You can check your keyword densities here: http://www.seositecheckup.com/

Input your website information and choose the drop-down option per the image example below:

The report will look something like this:

As you can see, the top three keywords are "seo", "do", and "yourself". That's because the top keyword phrase for that specific page is "Do It Yourself SEO". The other phrase, "Your Free SEO Resource" is secondary - and you'll notice the words "free" and "resource" appear as keywords as well. Prioritize your keywords and their densities appropriately, as is the case with the image example above.

Remember that this tool does not seem to recognize entire keyword phrases, only single words. So, keep that in mind when you are using this tool for keyword densities. Let me know if you have any questions or comments!