The discussion centers on identifying the quantity that represents rotational motion analogous to mass in linear motion, which is moment of inertia, denoted by the letter I. Participants mention angular momentum, angular frequency, and kinetic energy as related concepts but clarify that the correct answer is moment of inertia. The conversation highlights the importance of understanding these terms in the context of rotational dynamics. Overall, the role of moment of inertia is emphasized as crucial in analyzing rotational motion. Understanding these concepts is essential for grasping the principles of physics related to rotation.