Fear Kiting is a Warlock combat technique. It involves using the Fear spell on an enemy, casting damaging spells on the enemy and then, when the fear runs out, casting Fear on them again to repeat the process. This technique allows the Warlock to use damage over time spells or spells with long casting times that he/she normally would not be able to when in close combat. A skilled Warlock can keep an opponent "feared" so that the opponent can't even get one hit in.
This technique does have its limitations though, particularly in PvP. The opponent may use a trinket or racial trait to undo the fear effect or may have a spell which has given them resistance or immunity to fear. Also in patch 2.2.0 Banish, Seduction, Enslave Demon and Fear duration against PvP targets has been reduced to 10 seconds.
In PvE an enemy that is feared that runs too close to another enemy that is allied with it will cause the extra enemy to attack the warlock. This is particularly deadly in instances. A very skilled warlock can use Curse of Recklessness to avoid this by casting it on a feared enemy that is nearing an ally to make it temporarily immune to fear. The enemy will come running back to the warlock, averting disaster. Once the enemy is close again a different curse can be placed on the target, replacing the curse of recklessness and making it run away in fear again.