Immune: constructs, kami, ooze, plant, qlippoth, undead (usually), vermin; paladins of 3rd level or higher

The character is frozen in fear and can take no actions. A cowering character takes a –2 penalty to Armor Class and loses his Dexterity bonus (if any).

Marius, Scholai Armsmaster Says: Certain spells like Chill Touch and clerics with the Turn Undead feat can cause undead to cower. If a creature has the Panicked condition but has nowhere to run, they start Cowering. Since a cowering creature cannot take actions, it cannot take opportunity actions.  That means that you can perform combat maneuvers like trips, disarms, grapples, and dirty tricks to your heart’s content.  This can be particularly important if the cowering effect has a short duration.