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. Note the stun caused by the spell Symbol of Stunning doesn't really induce the conditioned stunned, it's actually considered dazed, as you aren't rendered helpless.

The heal spell can remove this condition.

List of abilities/spells that inflict the stunned condition:
 * Stunning Blow (6 seconds)
 * Severe Stunning Blow (This is a more powerful monster-only feat, it's duration varies, up to 8 seconds, and works on ranged attacks)
 * Power Word: Stun (2+1d6 seconds on players, longer on monsters)
 * Stat damage - if a monster or player hits zero constitution, they will be stunned for 6 seconds. (Red/Purple named immune)