Dhâranî(Sk.). In Buddhism—both Southern and Northern—and also in Hinduism, it means simply a mantra or mantras—sacred verses from the Rig Veda. In days of old these mantras or Dhâranî were all considered mystical and practically efficacious in their use. At present, however, it is the Yogâchârya school alone which proves the claim in practice. When chanted according to given instructions a Dhâranî produces wonderful effects. Its occult power, however, does not reside in the words but in the inflexion or accent given and the resulting sound originated thereby. (See “Mantra” and “Akasa”).
Source: H.P.Blavatsky - The Theosophical Glossary