Keyword density refers to a percentage that represents how frequently the target keyword appears relative to the number of words on the page.
Even though there is not an established rule for how many times a keyword should appear on a page, the common best practice is a keyword density of 1%.
That means that it is recommended that the top keyword be mentioned once for every 100 words of content.
For example, if you have a page with 1,000 words of content, the keyword should be mentioned about 10 times to be within the recommended density.
You also have to be careful not to over-optimize or do keyword stuffing, which implies using the top keyword more times than recommended.
The best way to avoid this is to write content that makes sense to the readers, not only to the search engines.