Keyword difficulty is a metric that measures how competitive a keyword is and how challenging it is to rank for it. It is displayed on a scale of 1 to 100 and can vary across different SEO tools. A high-difficulty keyword means there is a lot of competition, while a low-difficulty keyword means there is less competition. Understanding keyword difficulty is essential for making informed decisions about SEO strategy and choosing keywords that align with search volume, backlink profile, and content quality. Different SEO tools use varying methods to calculate keyword difficulty, and it is best to stick to one tool for each project.

source: Keyword difficulty in SEO guide: Everything you need to know