Which term refers to a riddle or mystery?

The term that refers to a riddle or mystery is "enigma." An enigma encompasses the idea of something that is puzzling, perplexing, or difficult to understand, which aligns closely with the notion of a riddle. It suggests a sense of hidden meaning or complexity that requires thought and insight to decipher, much like a riddle poses a challenge to one's reasoning abilities.

While all the terms provided can evoke ideas related to mystery or difficulty in understanding, "enigma" specifically emphasizes the sense of mystery at its core. For instance, a "puzzle" typically refers to a problem designed to test ingenuity, whereas a "conundrum" often implies a confusing problem or question that may involve a play on words. A "query" simply refers to a question or an inquiry, lacking the deeper implication of a riddle or a mystery. Thus, "enigma" stands out as the most fitting term for something that embodies the complexity and intrigue associated with riddles or mysteries.