120 VAC means 120 volts alternating current, the common household mains voltage in North America. It is a power-delivery standard, not a security control, but it matters in cyber security because many devices depend on it for charging, operation, or backup power. Knowing the input voltage helps determine whether equipment will run safely, whether a power supply is compatible, and whether a device can be deployed in a given environment without adapters, converters, or damage.
In real-world attacks and defenses, 120 VAC shows up wherever power is part of the threat surface. Attackers may target unplugged-but-powered infrastructure, tamper with wall outlets, or use compromised power accessories and inline devices. Defenders use the same knowledge to select proper power supplies, isolate sensitive systems with UPS units or surge protection, and audit physical infrastructure for unsafe or unauthorized hardware. In short, 120 VAC is a basic electrical specification that shapes device compatibility, safety, and the physical constraints around secure systems.