noun
grind; swot; person who studies obsessively
Colloquial, often slightly derogatory term for someone who studies excessively, especially for exams. Can be used as a noun to refer to the person.
彼はガリ勉だから、テストはいつも満点だ。
He's such a grind that he always gets full marks on tests.
noun, noun or participle which takes 'suru', intransitive verb
Refers to the act of studying intensely, often for exams. Used as a noun or with する to mean 'to cram'.
試験前は毎日ガリ勉するしかない。
Before exams, I have no choice but to cram every day.