Answer:
It means that in a comparison of two or more things, one is "smoother" and the other "rougher". Generally speaking to the texture of something. You could describe concrete as being rough, and a window as being smooth. We are programmed naturally to like smoother things as they seem more inviting to the touch, and less prone to natural defenses. You'd prefer an apple tree to a cactus as the apples are smooth, and the cactus is rough - built with natural defenses against predators.
All in all, it depends on what you are comparing, but is a comparison between the texture or feel of two or more objects.