Why it matters to a buyer
Every keyword tool defines and calculates difficulty a little differently, so a score of 40 in one tool is not the same as a score of 40 in another, and none of them fully accounts for a newer site's lack of existing authority, which makes even a "medium difficulty" term hard to win early. A buyer should treat it as a rough prioritisation aid for choosing what to target first, not as a precise forecast of whether a specific piece of content will rank.
How it is measured or applied
Difficulty scores are calculated mainly from the backlink profiles of the pages currently ranking on page one, since links remain the input most tools weight heaviest, with some tools folding in on-page and content signals as well. It is used by sorting a keyword list by difficulty against the site's actual current authority and choosing winnable targets first, then layering in judgement from a manual look at who currently ranks and how strong those specific pages are, since the score alone cannot see content gaps a competitor's page has left open.
