The letters D.O. actually stand for Doctor of Osteopathic Medicine, not Doctor of Osteopathy (see here: http://www.osteopathic.org/inside-aoa/news-and-publications/media-center/Pages/osteopathic-style-guide.aspx). Doctors of Osteopathic Medicine are complete physicians (they attend four years of medical school, go into residencies to specialize in a specific medical field, undergo board certifications and attend fellowships, etc.) and in addition to the traditional medical curriculum that overlaps with that taken by medical students seeking the Doctors of Medicine degree (M.D.), D.O. students also learn a form of manual therapy known as osteopathic manipulative treatment (OMT).