This is a special kind of a reasoning step. When a reasoner returns a cut reasoning step, it means that there are no more solutions left for the goal of the reasoning step. For example, if a relation is a function, i.e. it has only one value, and the query is for this value, then a reasoner might return one "normal" reasoning step with the answer, and then a cut reasoning step indicating that the search for more answers would be futile, at least within the indicated depth limit.