noun
research student
In Japanese universities, a non-degree student engaged in research under a supervisor, often as a preparatory step before entering a graduate program.
彼は大学院に入る前に研究生として一年間勉強した。
He studied for a year as a research student before entering graduate school.
大学院生 is a regular graduate student enrolled in a degree program, while 研究生 is a non-degree research student.
Compound of 研究 (research) and 生 (student).