undergraduate student; undergrad
Refers to a student enrolled in a university's undergraduate program (学部), as opposed to a graduate student (大学院生).
彼はまだ学部生で、来年卒業予定だ。
He is still an undergraduate and plans to graduate next year.
学部生のときは、よく図書館で勉強した。
When I was an undergraduate, I often studied in the library.
学部生 specifically emphasizes undergraduate status, while 大学生 can loosely include graduate students in casual speech.
Compound of 学部 (がくぶ, 'undergraduate department') + 生 (せい, 'student').