study book; book for learners
A book designed for self-study or classroom learning, often with exercises and explanations. More specific than 教科書 (school textbook).
I bought a Japanese study book and am studying on my own.
参考書 is a reference book or supplementary study aid, often used alongside a textbook, whereas 学習書 can serve as the main learning material.
Compound of 学習 (がくしゅう, 'learning') and 書 (しょ, 'book').