System resilience is the ability of a service to keep operating, or to recover quickly, after a failure, cyberattack, or other disruption. It goes beyond simple uptime: a resilient system can absorb damage, fail over safely, restore data, and return to normal without losing control of security or integrity.
In cyber security, resilience matters because many attacks cannot be stopped completely. Ransomware, API abuse, credential compromise, and configuration errors can still happen even in well-defended environments. Resilience reduces the impact by making backups usable, recovery procedures tested, access controls recoverable, and dependencies well understood. Defenders measure it with practices such as incident runbooks, restore drills, redundancy, segmentation, and monitoring of critical services. In compliance contexts like GDPR Article 32, resilience is part of proving that security measures are not just preventive, but also capable of sustaining and restoring processing when something goes wrong.