Maxfield wrote : "You know what a bump-map is, right?
A displacement map is similar"

Let me reply on that: a displacement-map looks similar to a bump-map but it's not quite the same.

A bump-map gives the impression of reliëf but a displacement-map actually changes the surface of the model.  The best way you can see that is by setting up a model with a monocolor diffuse shader and comparing two renders with a bump-map and a displacement-map. When you see a displacement-map from the side the surface really comes out, with a bump-map it doesn't, you can even see highlights on displacement-map, which isn't the case with bump-maps. I often use displacement-maps together with bump-maps. Bumps-maps can be used for the finer details.
For example: You can make dress or suit or another piece of cloth; with an displacement-map you can make a belt or button or pockets, and with the bump-map you make the cloth look like wool or leather or whatever.  This is very useful for dynamic cloths. With displacement -maps you can add extra details to model without being a modeller, you just can make your maps in Paintshop or photoshop. The possibilities are endless like you've seen in this thread!

-How can you improve things when you don't make mistakes?