Cyber Physical systems refer to new class of systems that features the integration of computation, communications and control technologies. The processing elements coordinate and communicate with sensors and actuators to monitor and affect the entities in the physical world. In this paper, we propose a domain model for CPS that tries to bring a clear terminology, by providing a common lexicon and taxonomy of the CPS domain. This model describes the most important concepts in regards to the CPS and the relationship between these concepts, in order is defining a modeling language aims at providing a means of communications between stakeholders in the engineering process.