Terminology questions are not generally off topic, as evidenced by a tag terminology of its own. To find out whether a question is a good fit for the stackexchange model, we have to ask ourselves whether this question has a single, objective answer.
With your question, this is not the case (but it isn't your fault). The
fold has been known by many names: fold, reduce. inject, aggregate, …. An answer could provide a name for the functional argument, but this name might not be known in other traditions that don't call it
fold. Therefore, an answer (that doesn't provide an answer for each of the different naming traditions) cannot be universally correct, and two answers that provide the correct answer for one of these traditions each would be equally correct, so there wouldn't be a clear candidate to accept. In short, this question is opinion-based.
There is also the small issue that (even within one such naming tradition) no universal name of the functional argument exists (which itself is a pretty clear name). When mathematically describing or implementing a
reduce function, I would simply call the argument
f, which is not satisfactory here.
The other question was answerable. It knew that a term had to exist. The asker tried to research this, and listed examples and possible terms, along with explanations why those terms do not sufficiently describe his concept. It showed that prior research on the asker's part had taken place (unlike your question where it was only clarified in the comments that this isn't quoted from an exam you are taking).