This software (generally) runs on Windows 95 and compatible Operating Systems. Windows 3.11 and below are 16-bit and are therefore excluded.
There are some oddities between the various flavours of windows, particularly incompatabilities for Win32 software that won't allow things to run on both Windows 95 and Windows NT/2000. Some programs designed for Windows XP will not run on versions.
Win32 may also refer to simulated Windows environments such as WINE.