a bump map simply alters the direction of the normal (based on a greyscale image/texture) to make it look as though it is lit differently. Displacement is the exact same except that it actually moves the point along the said normal by the calculated displacement.
check this
https://www.alanwoods.co.uk/personalr...rMaps.htm#Bump
Alan
Technical Director - Framestore
Currently working on: Your Highness
IMDB