An Intrusion Detection System (IDS) monitors network traffic or system activities to detect suspicious behavior, policy violations, or potential cyberattacks. It analyzes data in real-time using predefined rules, signatures, or behavioral patterns to identify threats like malware, unauthorized access, or data exfiltration. When a threat is detected, the IDS generates alerts to notify administrators for further investigation. While it doesn't block attacks, it plays a critical role in early detection and incident response within an organization’s security infrastructure.