A Simulation is a system that behaves similar to something else, but is implemented in an entirely different way. It provides the basic behaviour of a system, but may not necessarily adhere to all of the rules of the system being simulated. It is there to give you an idea about how something works. Example : Counter Strike - It looks and feels like you are in a warzone, but you are completely disconnected from the reality of warzone, and you can bend or break those rules as you see fit.

An emulation is a system that behaves exactly like something else, and adheres to all of the rules of the system being emulated. It is effectively a complete replication of another system. The rules are fixed, and cannot be changed, or the system fails. Example : Mobile Emulators