IBM invented computer emulation and introduced it with System/360 in 1964. They defined it as using special-purpose hardware and/or microcode on a computer to simulate a different computer.
Anything you run on your x86 (or ARM, MIPS, SPARC, Alpha, etc) does not meet that definition, and is a simulator, since those processors have only general-purpose hardware and microcode. Lots of people have other definitions of "emulator" which they've just pulled out of their a**, but since the System/360 architects invented it, I see no good reason to prefer anyone else's definition.
