self-study book; self-study guide
Refers to a book or guide designed for independent learning without a teacher.
I'm studying Japanese with this self-study book.
教科書 is a textbook used in formal education, whereas 独習書 is designed for independent learners.
Compound of 独習 (self-study) and 書 (book). The exact historical derivation is uncertain, but the meaning is transparent from its components.