A network blackout is a claimed or actual shutdown of business connectivity and services. It can mean users lose access to internal applications, identity systems, remote access, phones, cameras, or internet-facing services, either because of an outage, deliberate sabotage, or defensive isolation during an incident.
In cyber security, the term matters because availability is often as valuable as confidentiality. Attackers may threaten a blackout to pressure victims into paying, especially when they already have knowledge of network layout, remote-access paths, or configuration data. Defenders may also create a controlled blackout by segmenting or disconnecting systems to stop ransomware spread, protect backups, or contain suspicious activity. In both cases, the key issue is whether the loss of service is real, partial, or only being used as extortion language.