A cumulative exam is one that tests a student on all of the material since the beginning of the term. The word "cumulative" means that it results from a gradual growing in quantity by successive additions. A cumulative exam covers all the topics as they build on one another.
Final exams in education are usually categorized as either cumulative exams or a last-unit exams. Last-unit exams by definition cover less material but do not show what the student has retained over the course of the term. Satisfactory performance on a cumulative final indicates that the student has successfully retained information as it was covered and has built upon it, which is the goal of most courses.