A communications blackout is a period when normal digital connectivity is heavily restricted, degraded, or unavailable. It can result from deliberate throttling, network shutdowns, jamming, infrastructure damage, power loss, or overload. In practice, the outage may be partial rather than total, with some apps, carriers, or regions still working while others fail.
In cyber security, this matters because attacks and crises often depend on breaking coordination, not just stealing data. If messaging, cloud services, alerts, or authentication systems cannot reach each other, responders may miss warnings, delay decisions, or lose access to critical workflows. Defenders prepare for this by testing fallback channels such as radio, satellite, cross-carrier access, and offline procedures. A blackout is therefore both an attack pattern and a resilience problem: the goal is to keep essential communication alive when normal internet paths are stressed or cut off.