The discussion focuses on the nature of the space between Earth and the Moon, questioning whether it is simply empty or contains something more. Participants clarify that the term "interplanetary medium" accurately describes this space, distinguishing it from the "interstellar medium," which exists between stars. The conversation highlights a common confusion between these two concepts. Overall, the interplanetary medium is recognized as the region filled with low-density particles and radiation, rather than just black emptiness. Understanding these distinctions enhances comprehension of space's structure.