Key Term Density
Key term density describes the number of times that a particular key term appears in your page’s content relative to other text. It is an important consideration because it affects your page’s relevance for that key term. The logic, as always, is straightforward. If a page mentions a particular term many times, it must have content relevant to that term.
The real question is the amount of density you want. It used to be the case that more was always better until spammers caught on. Now, if your page contains a key term too frequently, it may be penalized for spamming. Of course, you still want to have the term appear on the page, but there is an optimal frequency for which you should aim. By most accounts, this density is approximately 5% to 7%. More than this and some engines may see it as spam; less and your page may not be viewed as very relevant for the term in question.
Testing your key term density is as simple as plugging the URL of your page into a Keyword Density Analyzer. Also, remember that gearing website content for search engines as well as visitors is a delicate process. Don’t inundate your page text with so many key terms that your optimization becomes obvious or you might turn off your visitors.