Understanding network traffic fingerprints is crucial for enhancing cybersecurity and network performance. This talk concisely explores passive network traffic fingerprints, discussing their definition, identification methods, and practical applications. We will cover techniques including deep packet inspection and flow analysis to capture and analyze traffic patterns. Real-world examples based on nDPI, an open-source DPI toolkit, will illustrate their use in intrusion detection, anomaly detection, and network monitoring, as well as other open-source tools such as Wireshark and Suricata.