What does "arcane" refer to?

The term "arcane" refers to knowledge that is not widely known and often requires special expertise or insight to understand. It suggests something that is obscure, secret, or understood by only a select few. This aligns perfectly with the idea of "something requiring secret or mysterious knowledge," indicating that the information is not readily accessible or commonly understood.

In contrast, the other choices imply a level of familiarity and openness that contradicts the meaning of "arcane." Common knowledge refers to information that is widely known and accepted by the general population, while widely accepted information suggests that a majority understands it clearly. Similarly, obvious facts are those that are clear and apparent to everyone, marking a stark difference from the esoteric nature of something described as arcane. Thus, the correct choice captures the essence of the term most accurately.