i would define them like this.
wing=mounted to trunk lid but only by a few spots,usually 2 spots,enabling air to pass under it as well as above.
i assumed we where not talking about airplane wings that is.
spoiler=also mounted to trunk lid,or any surface for that matter,but instead of mounting by a few places it mounts the complete length of the trunk lid.Does not enable air to pass under it.
Example would be a NASCAR.
Except the Plymouth Super Bird which had a wing.
Luggage rack=A device usually mounted to the roof or trunk lid of a vehicle to allow the carrying of items,usually bags of luggage,by the means of tie downs.
there is another type that utalizes a luggage rack and a wing together but the wing is usually not but a few inches from trunks surface.
technically it is still a wing since it allows air to flow under it..

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http://www.cardomain.com/id/88ciera_sc
1988 Cutlass Ciera SC
3.8L Sequential Fuel Injection
Horsepower- 160 @ 4000 RPM<factory lie
Torque(lb-ft)-215 @ 2750 RPM
Displacement- 3802cc
4 Speed Automatic
This WAS My Dad's Oldsmobile