Error rate is the percentage of requests that fail during a given period. In practice, it is a simple but important availability metric: if 100 downloads or API calls are made and 50 fail, the error rate is 50%. Security and operations teams track it because rising failures can indicate overloaded infrastructure, broken dependencies, misconfigurations, or active interference.
In cyber security, error rate helps distinguish normal traffic from service degradation and can support attack detection. Spikes may appear during denial-of-service attacks, authentication abuse, or backend failures caused by faulty defenses or blocked network paths. Defenders use it in monitoring, alerting, and incident response to see whether a platform is still usable, which functions are failing, and whether retries or failover are needed. A high error rate does not prove compromise, but it is a strong signal that availability and trust in the service are under stress.