What is the difference between a emulator and debugger?

A simulator is a software that duplicates some processor in almost all the possible ways.

An emulator is a hardware which duplicates the features and functions of a real system, so that it can behave like the actual system.

Usually the emulators and simulators are used for the testing of new architectures and also to give training in some complex systems.

A most famous example for a simulator is the flight simulator that simulates the functonalities of an aircraft.

Basically a simulator tests the program on the development processor (the processor on which we are working), while an emulator is used on the target processor (the processor for which the program is being written).