Keyword density is the percentage of times a specific keyword appears in your content relative to the total word count. If "digital marketing" appears 5 times in a 100-word article, the keyword density is 5%. It's a basic SEO metric that helps search engines understand what your content is about.
The sweet spot is 1-2% keyword density. Go too high and Google flags it as keyword stuffing — an outdated tactic that actually hurts your rankings. Go too low and search engines can't figure out your topic. Write naturally, place your keyword in the title, first paragraph, and a few times throughout the body, and you'll hit the right balance.