What is the message (WM_) for the window minimizing or deactivating?

Look up WM_ACTIVATE and WM_ACTIVATEAPP in MSDN.

It is actually part of WM_ACTIVATE.
The LOWORD of wParam holds more info on exact means of (de)activation.

The HIWORD of wParam is a boolean signifying being minimized or not.

switch(msg){    case WM_ACTIVATE:    switch( LOWORD(wParam) )    {         case WA_CLICKACTIVE:              // Activated by mouse click         case WA_ACTIVE:              // Activated by other means         case WA_INACTIVE:              // Deactivated    }    if ( HIWORD(wParam) )         // Minimized        break;} 

.Travois.