Stunned

A "Stunned" creature can’t take actions and is considered helpless. Generally for 6 seconds if from the Stunning Blow feat, but the duration will vary if from other sources.

Some stun effects, such as the spell Symbol of Stunning, don't make the enemy helpless. See helpless for details.

Preventing / curing stun

 * The spells Heal and Panacea can remove this condition.
 * The Path of Harmonious Balance Monk finishing move, Grasp the Earth Dragon, buffs parties against Stun attempts but cannot recover a stunned player.
 * Strength Domain: You always make your saving throw against Stun effects.

Feats

 * Stunning Blow (6 seconds)
 * Stunning Fist (6 seconds)
 * Dire Charge

Enhancements

 * Kukan-Do
 * Tomb of Jade (against Tainted creatures)
 * Jade Strike (against Tainted creatures)
 * Stunning Shield
 * Shield Champion

Spells

 * Soundburst (6 seconds)
 * Power Word: Stun (2+1d6 seconds on players, longer on monsters)
 * Salt Ray

Item effects
Stunning

Other sources

 * Severe Stunning Blow (This is a more powerful monster-only feat; its duration varies, up to 8 seconds, and works on ranged attacks)
 * Ability damage - when monsters or players reach zero constitution, they are stunned for 6 seconds. (Red/Purple named immune)