Corruption

Corruption is a level 2 warlock ability that damages over time.

Tips and tactics
Corruption is considered a bread and butter 'staple' ability of Affliction warlocks.

Corruption can be cast with your target behind you, and since it is instant cast it can also be cast while running. As such, this ability is excellent for kiting enemies. Since walking backward is much slower than running forward or strafe-running, it is always best to do one of the latter two things while attempting to kite something.

Trivia

 * Corruption is a basic Warlock spell in Hearthstone. The flavor text reads: "It starts with stealing a pen from work, and before you know it, BOOM! Corrupted!"
 * Corruption is one of Gul'dan's Basic Abilities in Heroes of the Storm.