Mathematics
Mathematics has a number of competing definitions, largely because of the ambiguity about the true nature of numbers. Some hunter-gatherer groups appear to barely have any concept of numbers whatsoever, perhaps because counting makes little sense unless objects have some degree of interchangeability. If you see each thing as unique, then what does it mean to count them?
On the other hand, numbers may represent relationships at their heart, which would make mathematics a way to study relationship. While most mathematics have become largely irrelevant to day-to-day life in the Fifth World, some communities see mathematics in this light and make a careful study of it for this reason.