Flee

Flee is a Control Impairing Effect on enemies, disabling them for a short amount of time. When enemies are fleeing they cannot attack or use abilities. Flee can be a useful when dealing with large groups of enemies, or very powerful enemies. Flee is caused by Fear abilities.

Also See:
Fear

The Following Is A List Of Each Class' Skills That Can Cause Enemies To Flee:

Barbarian Flee Abilities

Threatening Shout (Grim Harvest)

Demon Hunter Flee Abilities

Elemental Arrow (Screaming Skull)

Monk Flee Abilities

Breath of Heaven (Penitent Flame)
Cyclone Strike (Conflagration)