A working reference for the language of modern cybersecurity — organized by threat surface and defensive domain. Definitions are written for security professionals, technical managers, and informed practitioners who need precision without padding. Threat Actors and Motivation Advanced Persistent Threat (APT) A sophisticated, long-duration cyberattack campaign — typically state-sponsored — characterized by stealth, patience, and a specific high-value target. APT actors infiltrate networks and maintain persistent access for months or years before executing their objective.