Condition, Flat-Footed

At the start of a battle, before you have had a chance to act (specifically, before your first regular turn in the initiative order), you are flat-footed. You can’t use your Dexterity bonus to AC (if any) while flat-footed. Barbarians and rogues of high enough level have the uncanny dodge extraordinary ability, which means that they cannot be caught flat-footed. Characters with uncanny dodge retain their Dexterity bonus to their AC and can make attacks of opportunity before they have acted in the first round of combat. A flat-footed character can’t make attacks of opportunity, unless he has the Combat Reflexes feat.

A character who has not yet acted during a combat is flat-footed, unable to react normally to the situation. A flat-footed character loses his Dexterity bonus to AC and Combat Maneuver Defense (CMD) (if any) and cannot make attacks of opportunity, unless he has the Combat Reflexes feat or Uncanny Dodge class ability.

Characters with Uncanny Dodge retain their Dexterity bonus to their AC and can make attacks of opportunity before they have acted in the first round of combat.

Editor’s Note: reference from immediate action rules: You cannot take immediate actions while flat-footed.