The term 'simulator' refers to a device or software program that imitates real-world conditions for training purposes or experimentation. There are a number of synonyms that can be used in place of 'simulator,' including emulator, replicator, model, or mock-up. An emulator is a software program that mimics the behavior of a different system or device while a replicator copies the behavior of a system, object or process. A model can refer to a simplified version of a complex system that can be used to test hypotheses. Alternatively, a mock-up is a replica of a system that engineers design and evaluate before creating the real thing. All of these terms can be used interchangeably with simulator depending upon the context in which they are used.