An Operational Definition of Black Hole Interior Based on QES

This work proposes an operational definition of the black hole interior within a semiclassical effective framework. Rather than introducing a new fundamental theory, we clarify how existing concepts—such as quantum extremal surfaces (QES), island prescriptions, and boundary-based information recovery—can be consistently organized into a minimal definitional structure. The interior is defined operationally as a region whose degrees of freedom are not identifiable via volumetric localization but only through information-theoretic distinctions accessible from the boundary. This note aims to fix terminology and assumptions to facilitate future discussions, rather than to claim novel dynamics or mechanisms.