Focusing on the emergence and consolidation of this terminology, I make three arguments about the role of language in cybersecurity policy. First, I propose a new, politically consequential category of metaphor: foundational metaphors, implied by using particular labels rather than stated outright. These metaphors support specific ways to understand complex issues, provide discursive resources to some arguments over others, and shape policy contestation and outcomes. Second, I present a detailed empirical study of US military strategy and doctrine that traces the emergence and consolidation of terminology built on the “cyberspace domain.” This concept supported implicit metaphorical correspondences between the Internet and physical space, yielding specific analogies and arguments for understanding the Internet and its effects. Third, I focus on the rhetorical effects of this terminology to reveal two important institutional consequences: this language has been essential to expanding the military's role in cybersecurity, and specific interests within the Department of Defense have used this framework to support the creation of US Cyber Command.