A grammar book — a book that systematically explains the grammar of a language, often used as a study or reference resource.
日本語学習者向けの文法書を一冊買った。
I bought a grammar book for learners of Japanese.
授業の準備のために、古い文法書を参照した。
For lesson preparation I consulted an older grammar book.
図書館の文法書コーナーで参考書を探す。
I look for reference books in the grammar section of the library.