Disengage is a level 8 hunter ability that causes the player to leap backwards. It's useful in kiting enemies, reaching safe zones during a fight, or leaping away from hazards and area of effect attacks.
By using it near the ground after a long fall, it can also be used to reduce or prevent fall damage.
Disengage can be a potential liability in instances; it can easily add additional mobs to a fight if an inexperienced hunter Disengages without being aware of what's behind them first.
Jumping immediately before a Disengage will increase its travel distance. This can even be used for getting places more quickly, as the hunter can turn around mid-jump, use Disengage, then turn forward again and continue running.
If Disengage is used from high places, using a [Parachute Cloak] or other slow fall effect will extend the length of your flight by incredible amounts.
Trivia
Disengage is one of Greymane's basic abilities in Heroes of the Storm. It can only be used in worgen form, and in addition to rolling away, he shifts back into a human when using it.
Hotfix (2016-08-04): "Casting Disengage no longer causes your character to stop auto-attacking."
Patch 7.0.3(2016-07-19): No longer available to Survival.
Patch 5.4.0(2013-09-10): Now has a cooldown of 20 seconds (down from 25 seconds).
Undocumented change: No longer requires combat to use.
Patch 4.0.3a(2010-11-23): Now available at level 14, down from level 78, and has had its training cost updated.
Patch 3.1.2(2009-05-19): Cooldown reduced by 5 seconds.
Patch 3.1.0(2009-04-14): Cooldown increased by 5 sec.
Patch 3.0.3(2008-11-04): Now fails if you're rooted and is no longer on the global cooldown. Cooldown reduced to 25 seconds and no longer requires a target, though the hunter has to be in combat.
Patch 3.0.2(2008-10-14): This ability has been re-designed. Now leaps the Hunter backwards up to 13 yards. 30 second cooldown. Disengage now also only has one rank (rank 1).
Previously reduced threat against the target by a set amount.
Patch 1.2.0(2004-12-18): Disengage will cause the Hunter's target to immediately check for a new target.
[Farstrider], 
[Posthaste]
[Guide: Disengage]
[Parachute Cloak] or other slow fall effect will extend the length of your flight by incredible amounts.
[Moonkin Form] function of 
[Wild Charge] is similar to Disengage.
Patch 8.0.1 (2018-07-17): Changed back into a normal ability for Survival. Learned at level 8. 
Patch 7.1.5 (2017-01-10): Made available to Survival as a level 45 talent, replacing 
Patch 5.4.0 (2013-09-10): Now has a cooldown of 20 seconds (down from 25 seconds). 
Patch 4.0.3a (2010-11-23): Now available at level 14, down from level 78, and has had its training cost updated. 
Patch 3.1.2 (2009-05-19): Cooldown reduced by 5 seconds. 
Patch 1.2.0 (2004-12-18): Disengage will cause the Hunter's target to immediately check for a new target. 
Patch 0.12 (2004-10-11): Now usable against targets that are immune to physical attacks. 
