Jettison and Dump fuel - Do they have separate meanings?
In the context of fuel, jettisoning fuel would imply that the fuel is in a container that can be detached while in flight. In the linked image, the large tank below the main body is an external fuel pod that can be jettisoned. Jet with external fuel tank I believe in WWII that P51s would have drop tanks for escorts that would be jettisoned once an enemy encounter was expected.

Dumping fuel would simply mean that there is a type of valve located on the fuel tanks that can be actuated in some way such that the fuel can freely exit. Jetliner dumping fuel

To say differently, if one was holding water in a bucket, pouring the water on the ground would be 'dumping fuel' and simply dropping the bucket would be 'jettisoning fuel'

Reviewing the wikipedia article on Fuel Dumping, the author(s) make no such distinction between dumping vs jettisoning and seem to use jettison solely.

In the context of ATP, after reading the wikipedia article on fuel dumping, I believe that they are considered synonyms. I believe a non-pilot would go more along with my definition however. 

I answered in this manner as I believe that the OP is not a native English speaker and that clarification was needed as to distinguishing the two as they seem very similar. I am a native English speaker, but lay no claim to being a master of it.