Taxonomy in a review paper
It sounds to me like the reviewers were requesting that you include a set of “Index Terms” or “Keywords” for your paper, e.g., for IEEE, pulled from the list of IEEE Taxonomy or Standardized Keywords.
Excerpts the second link:

Help readers find your article quickly by using the right IEEE standardized keywords.
using the right keywords in your article can make your article more easily and reliably discoverable—which leads to a broader readership for your article.