A system outage is a period when services, servers, or internal tools are unavailable to users or staff. It can be caused by hardware failure, misconfiguration, maintenance problems, or a cyberattack such as ransomware. In practice, an outage does not always mean total loss of every system; it may affect only the applications that depend on the failed server or network segment.
In cyber security, outages matter because availability is a core part of business continuity. Attackers often aim to disrupt operations, not just steal data, and defenders must be ready to restore services quickly. Shared infrastructure can make a single compromise ripple across multiple teams or affiliated companies. Good defenses include segmentation, offline backups, monitoring, tested recovery plans, and clear dependency mapping so responders know which services will fail if one system goes down.