With the proliferation of Zero-Trust Architecture (ZTA) [1]-[3], a paradigm evolving from traditional, perimetercentric approaches to network security, there is a growing need for vocabulary that clearly identifies the nuances of existing design elements being implemented in ZTA. This paper introduces Zero-Trust Microsegmentation (ZTM) as a formal model to describe the practice of designating a gateway security component as the Policy Enforcement Point (PEP) within a ZTA. While the underlying technique is not new [4]-[6], defining it more explicitly mitigates conceptual overlap and clarifies how ZTM aligns with zero-trust principles by ensuring that east-west traffic is consistently inspected, logged, and subject to unified policy enforcement. Through a focused discussion on defining this practice-shifting routing to a gateway firewall capable of advanced, context-aware inspection-this paper demonstrates how ZTM simplifies rule management and auditing for operational teams, while providing organizational stakeholders with clearer insights into internal security measures. By offering a concise, standardized label for a widespread yet seldom-named practice, ZTM serves to streamline architectural discussions, strengthen regulatory compliance efforts, and support future developments in network segmentation strategies.