The professor is an academic rank at universities and other post-secondary education and research institutions in most countries. Literally, a professor derives from Latin as a "person who professes". Professors are usually experts in their field and teachers of the highest rank. Professors often conduct original research and commonly teach undergraduate, professional, or postgraduate courses in their fields of expertise. In universities with graduate schools, professors may mentor and supervise graduate students conducting research for a thesis or dissertation. In many universities, full professors take on senior managerial roles such as leading departments, research teams, and institutes, and filling roles such as president, principal, or vice-chancellor. The role of a professor may be more public-facing than that of more junior staff, and professors are expected to be national or international leaders in their field of expertise.