Which term describes knowledge that is only known by a select few?

The term that best describes knowledge that is only known by a select few is "esoteric." This word originates from the Greek word "esoterikos," meaning "inner" or "within." It refers to information or concepts that are not widely understood and are typically appreciated or accessible only to a specialized or small group of people. This could include intricate philosophical theories, advanced scientific principles, or certain artistic techniques that require specific knowledge or training to fully grasp.

In contrast, "universal" implies something that is applicable or known by everyone, which is the opposite of being exclusive to a select group. "Commonplace" indicates something that is ordinary or widely encountered, again not fitting the criteria of exclusivity. "Transparent" relates to clarity or openness, suggesting information that is easily available and understood by all, rather than restricted to a select few.