A Professor Emeritus is a full professor who retires in good standing. While technically this is the term for a male and women are known as Professor Emerita, women such as Germaine Greer are known by the masculine title. This title is also given to retired professors who continue to teach and to be listed; they may also draw a very large percentage of their last salary as pension. The title may also be given to full professors who have left for another institution but are still working full time. The concept has in some places been expanded to include also tenured associate professors. In some systems and institutions, the rank is bestowed on all professors who have retired in good standing, while at others it needs a special act or vote. Depending on local circumstances Emeritus Professors may retain their offices and/or other privileges in order to remain active in the academic community of an institution as a mentor or subject matter expert.

See for example the regulations regarding Professor Emeritus of The University of Edinburgh: http://www.aaps.ed.ac.uk/committees/senate/senate_pages/Functions/professor_emeritus_status.htm and in the general glossary of the University of Oxford http://www.ox.ac.uk/about_the_university/introducing_oxford/oxford_glossary/index.html

See the entries on Emeritus for the Latin meaning and Professor for the more general academic position.