Of the Ability Stats, Reflex represents dexterity, flexibility, accuracy, and ability to predict attacks.
As it modifies your physical ability to predict and dodge attacks, Reflex score is added to Armour Class saving throws.
Along with adding 1/2 Level to your To-Hit physical weapon rolls, you also add your Reflex score. A higher Reflex score means a greater potential to hit.
Reflex score is added to Agility skill check rolls.