A blue book for exams is a notebook used by students of many post-secondary schools in the United States to write essays and answer multiple short-answer questions. It typically contains about 20 lined pages and has a blue cover, hence the name "blue book". Blue book exams usually include one or more essays or short-answer questions, and sometimes the instructor provides students with a list of possible essay topics prior to the test itself. The first blue books were introduced by Butler University in Indianapolis in the late 1920s and were given a blue color because Butlers school colors are blue and white.
It is worth noting that there is also a digital testing application called Bluebook, developed by the College Board, which makes test day easier and faster for students and proctors. However, in the context of the question, it is more likely referring to the physical notebook used for exams.
