Feign Death allows the player to imitate dying. If successful, a player can reduce his aggro with an NPC. After five minutes of successfully feigning death, all NPCs will forget about the player and continue as if never attacked. The ability to feign death as a skill (rather than a spell that can fail or be interrupted) makes monks an especially welcome member to a hunting party or raid, as it makes them very successful pullers.
Feigning death can be broken if the player if hit by a spell that an NPC started casting before the player feigned, or if an area-of-effect (AoE) spell goes off within your range. It is possible to purchase alternate abilities that allow feigners to continue to feign through spells, and to make it occur more reliably.
One simply needs to stand to cease feigning death.