The term emulation is used in computer science to denote a range of techniques all of which involve using some device or program in place of a different one to achieve the same effect as using the original. The term "simulation" is often confused with - and sometimes even used as a synonym for - emulation, but we distinguish between the two terms here by noting that a simulation describes what some other thing would do or how it would act, whereas an emulation actually does what that thing would do. For example, an aeroplane simulator does not actually fly. That is, simulation generally involves the use of a model to understand, predict or design the behaviour of a system rather than the practical recreation of that system's capabilities. In contrast, emulation is generally used to create a surrogate for the system being emulated.
For preservation purposes, the focus is on emulating older, obsolete computers on future computers. In this context, emulation would enable future computers to "impersonate" any obsolete computer, virtually recreating the obsolete computer and thereby allowing its original, obsolete software to be run in the future. This would allow the original rendering programs for obsolete digital formats to be run on future computers, under emulation.
Emulation is a useful strategy when interacting with the original software is important and when no suitable migration path is available.