False Positive: A system mistakenly flags benign or normal activity as suspicious or malicious. While this doesn't pose a direct threat, a high number of false positives can lead to alert fatigue, which is when genuine alerts are ignored due to a large number of false alarms, potentially leading to overlooked real threats.

False Rejection Rate (FRR): The likelihood that a biometric security system will incorrectly reject an access attempt by an authorized user. It is one of the key metrics used to evaluate the accuracy of biometric systems, the other being the False Acceptance Rate (FAR). Balancing FRR with FAR is crucial to ensure both security and usability.

Faraday Cage: An enclosure used to block electromagnetic fields. It is typically formed by a conductive material or a mesh of such material. Named after the English scientist Michael Faraday, who invented them in 1836, Faraday cages work by distributing charge or radiation around the cage's exterior, thus canceling out electric charges or radiation fields inside the enclosure. Faraday cages are used to protect electronic equipment from lightning strikes and electromagnetic interference (EMI) as well as to prevent EMI from emanating from electronic devices. They are also used in secure environments to prevent eavesdropping or data theft via electronic means.

Fault Injection: The deliberate introduction of faults or errors into a system to test its resilience and to validate its error detection and recovery capabilities. It can simulate various failure conditions and helps in understanding how a system behaves under abnormal conditions.

Fault-Resistant Network: A fault-resistant network, often synonymous with fault-tolerant networking, incorporates design principles and technologies aimed at achieving continuous network operations despite failures of individual components. Such networks utilize redundancy, diverse routing paths, and self-healing mechanisms to prevent single points of failure and ensure service availability.

Fault Tolerance: The ability of a system to continue functioning properly in the event of a hardware or software failure. This is achieved through the incorporation of redundancy in the system's components or through techniques like replication of tasks so that in the event of a component failure, the system's operation continues without disruption.