Hola, no es que nadie te ayude, es que ya hay un montón de foros sobre esa misma pregunta.
Si miras en cuanquiera de ellos verás que el undergraduate es el estudiante universitario y el graduate es el licenciado. Ya ha terminado los estudios universitarios y ahora puede hacer estudios superiores: master o doctorado.
No creo que sea correcta tu definición de graduate, Yoliyoli. Si dices solo Graduate student (vs High School graduate, por ejemplo) se entiende que es un estudiante de posgrado. Mira lo que dice Wikipedia: A graduate school (sometimes shortened as grad school) is a school that awards advanced academic degrees (i.e. master's and doctoral degrees) with the general requirement that students must have earned a previous undergraduate (bachelor's) degree... Many universities award graduate degrees; a graduate school is not necessarily a separate institution. While the term "graduate school" is typical in the United States and often used elsewhere (e.g. Canada), "postgraduate education" is also used in some English-speaking countries (Australia, Canada, Ireland, India, New Zealand, Pakistan and the UK) to refer to the spectrum of education beyond a bachelor's degree. Those attending graduate schools are called "graduate students" (in both American and British English), or often in British English as "postgraduate students" and, colloquially, "postgraduates" and "postgrads". Degrees awarded to graduate students include master's degrees, doctoral degrees, and other postgraduate qualifications such as graduate certificates andprofessional degrees.
Undergraduate educationFrom Wikipedia, the free encyclopedia
Undergraduate education is the post-secondary education previous to the postgraduate education. It includes all the academic programs up to the level of a bachelor's degree. For example, in the United States an entry level university student is known as an undergraduate, while students of higher degrees are known as graduates. In some other educational systems and subjects, undergraduate education is post-secondary education up to the level of a master's degree; this is the case for some science courses in Britain and some medicine courses in Europe.