What aspect of SEO does the term "keyword density" refer to?

The term "keyword density" refers specifically to the frequency of keywords used within a piece of content compared to the total word count of that content. This measurement helps determine how often a particular keyword appears, expressed as a percentage of the total words. It's an important factor in search engine optimization (SEO) because search engines analyze keyword density to understand the relevance of a webpage to specific search terms.

Maintaining an appropriate keyword density can help improve a site's visibility on search engine results pages, as it can indicate to search engines that the content is focused on specific topics related to the keywords. However, it's also crucial to balance this density with natural language use to avoid keyword stuffing, which can negatively impact ranking.

In contrast, the other options do not accurately describe keyword density. The number of images on a webpage, links to other websites, and the size of web content relate to different SEO aspects, such as image optimization, link-building strategies, and content quality, respectively. These elements are important for overall SEO, but they do not pertain specifically to keyword density.