KD
An Ahrefs score from 0 to 100 estimating how hard it is to reach the first page of Google for a search term.
KD stands for Keyword Difficulty. It is calculated from the backlinks pointing at the pages ranking there now.
It counts links only, not how well those pages answer the search, so a high score can hide a first page of thin or dated results. Treat it as a guide, and look at the results themselves before deciding a term is out of reach.