Reaction

A Reaction is an instantaneous response to someone else's Action or an occurrence you've prepared for, you may even use a Reaction when it's not your turn. Examples of Reactions include making a Perception check to notice a bounty hunter sneaking up behind you and instantly activating a Force Power to absorb damage from an incoming blaster bolt.
You may take a number of Reactions equal to your Dexterity Modifier in between your turns. You may only take a single Reaction to any one Action or effect. A Reaction is always resolved after the Action that triggered it, though some Reactions (such as the Negate Energy Force Power, or the Block and Deflect Talents) can affect the outcomes of the Action that triggers a Reaction.

• Special: Attacks of Opportunity are a type of Reaction. Without the Combat Reflexes feat you are only allowed one Attack of Opportunity in between your turns, regardless of how many Reactions you may have.