Keyword density (SEO) is the number of times a keyword or key phrase appears on a web page as a percentage of the total number of words on the page.
There’s really no optimal keyword density for your content, but if it’s so dense as to look like you’re stuffing keywords into your copy for the sake of optimization, you might draw a penalty.
Some experts peg between 0.5 and 2.5% as good percentages to strive for and something as high as 4% as likely to draw a penalty, but that’s not what really matters.
Use Keywords Naturally
What does matter is that you write for your reader, not for the search engine. It’s good if your keyword is in your headline and SEO title, and a few of your subheads, but never distort natural copy to accommodate a keyword.
If you’re writing naturally, you’ll tend to use synonyms and vary your phrasing, and Google (among other search engines) has begun to look for this.
Context Is Important
They’re getting better at understanding context – and you can help them by using well-written, informative content that includes words they would expect to find in that context.
If you’re writing about German Shepherd dogs as pets, for instance, the search engine might like to see “working dog”, “puppy”, “black and tan”, “kennel”, “AKC”, and so on.
If you’re writing about German Shepherds as police dogs, the search engine might know better what to return if you include words like “police”, “police dog”, “K-9”, “attack dog”, “bite training”, and so on.
You may hear the terms ‘co-occurrence” and “proof words” in connection with content that includes more synonyms and related terms. These are good things, and occur naturally in well-written copy that’s meant to fulfill a searcher’s question.