Reference books are typically resources like
Almanacs.
Atlas & Maps.
Bibliographies.
Biographical Resources.
Dictionaries.
Directories.
Encyclopedias.
Handbooks
We also include textbooks in this category as well as test prep. We have published a wonderful book through Micro Publishing Media (MPM) to help students prepare for the SAT. It is one of the best books to help with both the math and the reading sections of the new test.