Cyber-Physical Systems (CPS) involve communication, computation, sensing, and actuating through heterogeneous and widely distributed physical devices and computational components. The close interactions of these systems with the physical world places events as the major building blocks for the realization of CPS. More specifically, the system components and design principles should be revisited with a strictly event-based approach. In this paper, a concept lattice-based event model for CPS is introduced. Under this model, a CPS event is uniformly represented by three components: event type, its internal attributes, and its external attributes. The internal and external attributes together characterize the type, spatiotemporal properties of the event as well as the components that observe it. A set of event composition rules are defined where the CPS event composition is based on a CPS concept lattice. The resulting event model can be used both as an offline analysis tool as well as a run-time implementation model due to its distributed nature. A real-life smart home example is used to illustrate the proposed event model. To this end, a CPS event simulator is implemented to evaluate the developed event model and compare with the existing Java implementation of the smart home application. The comparison result shows that the event model provides several advantages in terms of flexibility, QoS support, and complexity. The proposed event model lay the foundations of event-based system design in CPS.