Windows on Windows (WOW) — is a system component, which enables running apps that using legacy 16-bit version of Windows API (Win 16) in 32-bit versions Windows NT.
WOW is implemented with the help of NTVDM and win16api stubs. NTVDM is used for running 16-bit code, and win16api stubs thunk legacy 16-bit APIs to their newer 32-bit equivalents.
Usually, WOW is needed for old 16-bit installers.
29-03-2018 Aleksandar Andrejevic (NTVDM developer) announced that he plans to work on WOW.
Why 16-bit apps work in the Wine?
In the Wine, running of 16-bit apps depends on kernel module ldt16, whereby emulate 16-bit code.