Keyword density is the percentage of incidences of a given keyword on a web page relative to the total word count on that page.
Keyword density was once a key factor in determining a page’s search ranking, and the more times a keyword appeared in content, the higher the page would be ranked.
In the internet’s earlier years, high keyword density meant a web page would appear higher ranked in searches for that keyword. It was assumed that if a keyword appeared more on a given page, that page would be more likely to be relevant to the user’s search and have more relevant content. Following that logic, naturally, such a page should be ranked higher and appear higher on a search engine results page (SERP), so that users would find it more readily.
However, the supposition of relevance was only true if a page was written naturally and optimized for readability and quality of content. Often, that page ranking method was exploited through keyword stuffing, which involves overuse of a keyword in content, to the detriment of quality.
Currently, search engines lower the rank of pages that try to exploit keyword stuffing. For search engine optimization (SEO), the prevalence of a keyword must be balanced because the analysis used to rank pages is much more sophisticated than it once was.
Lots of effort goes into preventing invalid content from appearing prominently in search results. Both keyword stuffing and the low-quality writing that stems from it can lead to a site being marked as unscrupulous. A search engine may designate such a site as part of a bad neighborhood. The best approach is to write content for users, not search engines, while naturally and appropriately using valued keywords.
A keyword density of between one and three percent is best for SEO. You can check keyword density by dividing the number of times a keyword appears on a page by the total number of words on the page and then multiplying by 100. Keyword phrases should be treated as a single word for the calculation. Keyword density checking tools are also available.