postgraduate in British English
(pəʊstˈɡrædjʊɪt), postgrad or post-grad (ˌpəʊstˈɡræd)
noun1. a student who has obtained a degree from a university, etc, and is pursuing studies for a more advanced qualification
2. (modifier) of or relating to such a student or to his or her studies
Also (US and Canadian): graduate