Which term might indicate something that occurs twice?

The term that indicates something that occurs twice is "bilateral." In medical terminology, "bi-" is a prefix that means two. Therefore, when it is used in conjunction with an anatomical term or concept, it signifies that the condition or reference involves both sides or two instances. For example, "bilateral" often refers to organs or structures that are paired, such as bilateral lungs or bilateral symptoms, indicating that both sides of the body are affected or involved.

The other prefixes represent different quantities: "mono-" refers to one, "tri-" indicates three, and "quadri-" signifies four. Therefore, they do not convey the concept of something happening twice as effectively as "bilateral" does.