Simulation fidelity is how closely a model matches the real system it represents. In cyber security, that means how accurately an emulator, sandbox, network lab, or digital twin reproduces software behavior, timing, dependencies, and failure modes.
Fidelity matters because security decisions are only as good as the environment being tested. A low-fidelity model may miss malware evasion tricks, race conditions, protocol edge cases, or detection gaps. A high-fidelity simulation can help defenders safely test patches, tune intrusion detection, validate incident response playbooks, and study attacker behavior before deploying changes to production. But higher fidelity usually costs more CPU, memory, data, and setup complexity. The practical goal is not perfect realism; it is enough realism to answer the security question at hand without creating false confidence.