The "Measurement Problem" in quantum mechanics refers to the challenge of understanding how and when a quantum system transitions from a state of superposition, where it can exist in multiple states simultaneously, to a single, definite state upon measurement. This issue arises because the act of measuring seems to influence the system, leading to different outcomes depending on the measurement process. This problem is closely related to concepts like wave function collapse and the role of the observer in quantum mechanics. Various interpretations, such as the Copenhagen interpretation and Many-Worlds interpretation, attempt to explain this phenomenon, but no consensus has been reached among physicists.