This is not a stupid question at all as there is actually a difference. With a 4WD drive car when you select 4WD both front and rear axles are driven simultaneously. With a AWD car such as a Subaru Impreza power is transfered to the axle wich has most grip and is only truly 4WD for a split second whilst power is transfered between axles. Normally a 4WD will have a low ratio gear box too and an AWD car wont. But even a 4WD is not trully 4WD unless you can lock the differential.
Hope this helps