1. An emulator is a system which implements another system's functionality so as to serve as a usable replacement. Examples include in-circuit emulators for hardware components, or software emulators for game system hardware. In each case, the emulator is a usable replacement for the original system.
2. WINE reimplements the functionality of Windows, as exposed by the Windows ABI, as software running on Linux.
3. The combination of WINE and Linux is in fact a usable replacement for Windows.
4. Which means that WINE running on Linux conforms to the above definition of an emulator for the Windows system.
5. Therefore, WINE running on Linux certainly is an emulator for the Windows system.
> Wine (originally an acronym for "Wine Is Not an Emulator") is a compatibility layer capable of running Windows applications on several POSIX-compliant operating systems, such as Linux, macOS, & BSD. Instead of simulating internal Windows logic like a virtual machine or emulator, Wine translates Windows API calls into POSIX calls on-the-fly, eliminating the performance and memory penalties of other methods and allowing you to cleanly integrate Windows applications into your desktop.
Except it isn't true. Wine does absolutely do a lot more than just direct API call translation (the systems are too different for that) - otherwise there weren't a whole heap of processes (wineserver, explorer.exe, etc.) needed to run any single program trough Wine.
#1 defines a compatibility later, rather than an emulator, in my mind. Emulators typically perform some form of translation from the original (completely unsupported) code to something the host can understand. Wine implements PE binary support natively in Linux.
It may not be an emulator in a highly specific & technical sense used by and useful to a small group of experts. It is an emulator in the general and widely-recognized sense of "software that runs software originally intended for a different, incompatible system."
You see this all the time when a jargon word enters the general non-specialist vocabulary. It doesn't make either usage wrong, though it can be confusing sometimes if the contexts can be difficult to distinguish. In this case that's unlikely so just give it up please.
Honestly the quirk where that is its name could be a really useful entry point for educating non-specialist readers on the different technical approaches used to solve this problem! I never see that though, this is only ever used as a wellackshully on internet forums. It sucks.
Honestly I don’t even understand the narrow sense in which you could say WINE is not an emulator.
There was supposedly a naming discussion in 1993 which resulted in “WINE is not an emulator”. Maybe this was to remind people that you still needed an x86 processor (WINE is not an x86 emulator), or maybe it was born from the idea that WINE does not emulate Windows—maybe it “provides a compatibility layer” or “reimplements the Windows interfaces”.
The Windows APIs are not so well-specified that a mere reimplementation of them would run so much software as WINE does.
