The Nuffic Glossary is a list with explanations of terms used in Dutch education.
As a noun, a graduate is a person who has recently earned a degree, generally a bachelor's degree. 'Graduate' as an adjective is used by Americans to refer to all students who are pursuing either a master's degree or a PhD: i.e., 'graduate students', who go to 'graduate school'.
Outside America, all students in these categories are called 'postgraduate students'. 'Graduate' and 'postgraduate' mean the same thing. The word 'postgraduate' offers the advantage that everyone understands it correctly even if they use the other term themselves. The same cannot be said for 'graduate'.
The Bologna Declaration is a reason to opt for 'graduate', however, especially in an EU context. The Bologna Declaration refers to two cycles of higher education, which it calls the 'undergraduate' and the 'graduate' cycles. In any case, you must use one term or the other. They are synonyms so you cannot use both to mean two different things.