You disperse into pure Shadow energy, reducing all damage taken by 90%. You are unable to attack or cast spells, but you regenerate 6% mana every 1 sec for 6 seconds.
Dispersion can be cast while stunned, feared or silenced and clears all snare and movement impairing effects when cast, and makes you immune to them while dispersed.
Reduces all damage by 90%, and you regenerate 6% mana every 1 sec for 6 seconds. Cannot attack or cast spells. Immune to snare and movement impairing effects.
You disperse into pure Shadow energy, reducing all damage taken by 90%. You are unable to attack or cast spells, but you regenerate 6% mana every 1 sec for 6 seconds.
Dispersion can be cast while stunned, feared or silenced and clears all snare and movement impairing effects when cast, and makes you immune to them while dispersed.
Dispersion is a defensive priest ability that is available via the highest talent of the Shadow tree. Dispersion protects the priest by reducing the damage taken by 90% for 6 sec. Meanwhile the priest will regenerate 6% mana every second up to 36% of mana in total. Due to its relative low cooldown and free cast, Dispersion is an excellent regeneration spell. Dispersion can be cast while stunned, feared or silenced, which makes it very useful in PvP as well.
It has many uses in PvE besides just regenerating mana, you can also use it to soak large (AoE) hits that would reduce a fully geared tank into a red stain on the floor.
Edit
Patch 3.2.0 (2009-08-04): Cooldown reduced to 2 minutes, down from 3 minutes. 
