Check out this Jump-Disengage article over on wow.com.

If you want to see an amazing use of this ability in practice, check out Ensidia's world first kill of Mimiron Hard Mode (25). The boss is almost dead, most of the ranged are surrounded by fire, and the hunter (Munken) executes a perfect jump-disengage over to one of the few safe spots to get some more shots in at the very end (skip to about 1:55 to see it). Here's a link to the video: http://www.youtube.com/watch?v=zsa8FKEOqXM