A forgiving form of ROUGE-N that enables skip-gram matching. That is, ROUGE-N only counts N-grams that match exactly, but ROUGE-S also counts N-grams separated by one or more words. For example, consider the following: - reference text: White clouds - generated text: White billowing clouds When calculating ROUGE-N, the 2-gram, White clouds doesn't match White billowing clouds . However, when calculating ROUGE-S, White clouds does match White billowing clouds.