Keyword difficulty is an SEO tool's estimate of how hard it would be to rank on the first page of search results for a search term, usually on a 0–100 scale.
Most tools base it on how many strong sites link to the pages already ranking. Each tool calculates it differently, so scores aren't comparable between tools.
Low-difficulty terms are usually long-tail searches with smaller volume but clearer intent.
Why it matters for a launch
A new site with few backlinks should aim for low-difficulty, specific searches first; competitive terms come later.