Psychic Scream is a priest talent available at level 60. It causes nearby enemies to run away in fear. There is a chance to resist it that increases as the enemy becomes higher level than the caster. This resistance becomes important when depending upon psychic scream to escape combat and psychic scream fails. Be careful when using it so fleeing enemies do not wake up additional mobs on their return.
Combined with [Mind Flay], shadow priests can tie enemies to them so they don't have the ability to run further than 20 yards and escape to aggro other mobs. Mind Flay also counts as a dot and has a reduced chance of breaking the fear.