[Closed] Windows SDK Question

I use GetProp()/SetProp() with an Atom. Under x64 the ‘lpString’ of SetProp() is 64 bit long.

The MS doc says: “The atom must be placed in the low-order word of lpString; the high-order word must be zero.”
See: https://technet.microsoft.com/de-de/ms633568

Usually I use

SetpProp(hwnd, (LPCTSTR) MAKELONG(atom,0), data)

to set the lpString parameter which seem to ok under x32. But what is the definition of a “word” under x64 ?