Final answer:
An association class represents a many-to-many relationship between two classes, serving as a link that can store additional information unique to each pair of instances.
Step-by-step explanation:
A class that represents a many-to-many association between two other classes in object-oriented programming is called an association class. This concept is quite fundamental in understanding how objects can interact in a system. Association classes are pivotal when it comes to realizing relationships where multiple instances of one class are associated with multiple instances of another. An example could be a scenario in which you have a class called Student and another called Course. A many-to-many relationship exists because a single student can enroll in multiple courses, and a single course can include multiple students. The association class, which might be named Enrollment, serves as the link between the two, holding additional information that pertains to each unique student-course pairing, such as grades or dates.