32-bit apps running on 64-bit Windows run using a Windows component called "WoW64". There is another compatibility layer used to run 16-bit apps on 32-bit Windows called "WoW".
Neither "WoW64" nor "WoW" are usually referred to as "hypervisors". That term is usually reserved for systems which run a full operating system using CPU virtualisation technology – Hyper-V, VMWare, VirtualBox, Xen, KVM, etc.
By contrast, WoW64 and WoW are rather thin translation layers. WoW64 just intercepts the 32-bit API calls, translates the parameters, invokes the 64-bit API, and then translates the results back to 32-bit. (WoW does basically the same thing for 16-bit calls to 32-bit.) This is possible because all of the Win32 API calls have Win64 equivalents (likewise, most Win16 API calls have Win32 API equivalents, except for a handful of obscure Win16 APIs which newer versions of Windows don't support.)
WoW runs under NTVDM which uses virtual 8086 mode, so you might call WoW a "hypervisor" in that sense (although the hypervisor is really NTVDM not WoW.) But WoW64 does not use any virtualisation technology at all.
Well, those 32-bit apps run in a hypervisor. The compatibility is so good because you have both 64-bit and 32-bit Windows in your 64-bit installation.
32-bit apps running on 64-bit Windows run using a Windows component called "WoW64". There is another compatibility layer used to run 16-bit apps on 32-bit Windows called "WoW".
Neither "WoW64" nor "WoW" are usually referred to as "hypervisors". That term is usually reserved for systems which run a full operating system using CPU virtualisation technology – Hyper-V, VMWare, VirtualBox, Xen, KVM, etc.
By contrast, WoW64 and WoW are rather thin translation layers. WoW64 just intercepts the 32-bit API calls, translates the parameters, invokes the 64-bit API, and then translates the results back to 32-bit. (WoW does basically the same thing for 16-bit calls to 32-bit.) This is possible because all of the Win32 API calls have Win64 equivalents (likewise, most Win16 API calls have Win32 API equivalents, except for a handful of obscure Win16 APIs which newer versions of Windows don't support.)
WoW runs under NTVDM which uses virtual 8086 mode, so you might call WoW a "hypervisor" in that sense (although the hypervisor is really NTVDM not WoW.) But WoW64 does not use any virtualisation technology at all.