Cyber defense is the set of security activities used to prevent, detect, and respond to attacks on systems, networks, and data. It combines controls such as hardening, patching, authentication, logging, threat detection, incident response, and recovery planning. In practice, cyber defense is not one tool but a layered process that reduces attacker access and limits damage when a breach occurs.
It matters because most real-world attacks exploit weak configuration, stolen credentials, vulnerable software, or poor monitoring. Defenders use cyber defense to spot suspicious behavior early, contain malware or intrusions, and restore trusted operations quickly. In AI security, the term also covers protecting models, prompts, training data, and connected infrastructure so an attacker cannot manipulate outputs, steal sensitive data, or use the system as a new attack path.