A critical transmission facility is a power-transmission asset whose loss, damage, or outage could create major grid instability. These sites are identified because they sit at high-impact points in the bulk power system, where even a single disruption can affect power flow, protection systems, or recovery options across a wider region.
In cyber security, the term matters because these facilities are part of a cyber-physical attack surface. An attacker may target them directly through sabotage, or indirectly by interfering with monitoring, access control, communications, or operational planning. Defenders use risk assessments, asset classification, and layered physical and digital controls to decide which sites need the strongest protection. The goal is to reduce the chance that a localized compromise becomes a cascading reliability failure.