A 0–100 score from third-party SEO tools (Ahrefs DR, Semrush KD, Moz, others) estimating how hard it is to rank in the top results for a query. Each tool's formula differs but typically combines the link metrics of pages currently ranking with content depth signals. Useful for relative comparisons within a single tool, less so as an absolute "your site can rank in N months" figure. Keyword-difficulty scores ignore your own site's existing topical authority — a strong site in the niche may rank for a "high difficulty" keyword far easier than the score suggests.