A digital twin, which is used for the purpose of enhancing the security of a cyber-physical system, is a virtual replica of a system that accompanies its physical counterpart during phases of its lifecycle, consumes real-time and historical data if required, and has sufficient fidelity to allow the implementation of the desired security measure.

Book: M. Eckhart, A. Ekelhart. Digital Twins for Cyber-Physical Systems Security: State of the Art and Outlook, 2019. [Springer]