A network intrusion detection system (NIDS) is a security measure designed to monitor network traffic for suspicious activity and potential threats. NIDS analyzes data packets traversing a network to identify patterns indicative of malicious behavior, such as intrusion attempts or security breaches. When suspicious activity is detected, NIDS can generate alerts to notify network administrators, facilitating quick action to mitigate threats. Its primary function is to enhance network security and protect sensitive information from potential attacks.