Keyword Density is the number of times, or percentage, a particular keyword appears in the content on a web page compared to the over all number of words on the page. In the past, keyword density was an important part of SEO. In using just the right density, usually between 2% to 9%, helped to rank your web page higher for that keyword.
Matt Cutts of Google indicates that Google does not have a magical formula for measuring keyword density. The approach, especially after the Panda updates from last year, is to make sure your keywords and keyword phrases are natural and flowing. You don’t want to say, “Boat covers are important because boat covers keeps your boat dry and boat covers should be considered for this reason.” Google is looking more for the natural flow and use of the keyword in the content. They also measure the use of the keyword throughout your site, and not as much on the main landing page. So there needs to be natural and consistent use of the keyword on all pages. It is important to vary the use of the keyword, using other terms to explain the same thing. For example: “Boat covers are important because they help to cover your boat and keep it shielded from the weather.”
Your main keyword should be used at least once in your title tag, and possibly a few times in your meta description. Google no longer considers your keywords in the meta description for ranking purposes, but they do bold them in the description of the search results. Bolded words will give you a little more of an edge for catching the eye of the our customer over competitors who are not using the search keyword in their description.