Reflex refers to the limbs bending away from the shooter at the tips, like a recurve. Reflex adds zip to the bow. Deflex is whenthe limb bending back towards the shooter just off the riser/handle. Deflex helps with hand shock resulting in a smoother bow. To put it in perspective, the limbs make a S shape.

Here is a reflex deflex. Its a mild reflex deflex design. There are all degrees of reflex and deflex that can be put into a bow.