Keyword difficulty in SEO is a measure of how difficult it is to rank for a particular keyword or phrase on search engines. This metric is often used by SEO professionals to determine which keywords to target in their optimization efforts. Keyword difficulty takes into account factors such as the number of websites competing for the keyword, the quality of those websites, and the strength of the keyword in terms of search volume and relevance to the topic. By analyzing keyword difficulty, SEO professionals can determine which keywords are likely to be the most effective for their optimization efforts.