A kind of Vidyā (occult science);
that Vidyā. in which the kuśa (grass) is first treated by chanting Mantras; then the patient is treated with it, which makes him free from the ailment.
yā darbhe darbhaviṣayā bhavati vidyā, yayā darbhairapamṛjyamāna āturaḥ praguṇo bhavati.
(VyaBhā 2439 Vṛ)