What exactly is a "displacement map"? Is that the same thing as a "trans map"? If not, how do you use a "displacement map" in the material room?  And what is it "displacing"?

"It is good to see ourselves as others see us. Try as we may, we are never
able to know ourselves fully as we are, especially the evil side of us.
This we can do only if we are not angry with our critics but will take in good
heart whatever they might have to say." - Ghandi