Postgraduate is the name for someone who is doing further education, after he or she graduated from university. A typical form of this kind of education is a doctoral thesis, or Ph.D. Another such degree is probably the Master level of the revised Bologna system. Masters can be done in about 1.5 years after doing a bachelors degree, theses usually take 3–4 years, after the master level.
Postgraduate education Facts for Kids. Kiddle Encyclopedia.