The material below is Open Game Content from a 3PP Source
Weapon Finesse (Combat)
You are trained in using your agility in melee combat, as opposed to brute strength.
Benefit: With a light weapon, rapier, whip, or spiked chain made for a creature of your size category, you may use your Dexterity modifier instead of your Strength modifier on attack rolls. If you carry a shield, its armor check penalty applies to your attack rolls.
Special: Natural weapons are considered light weapons.
The material below is Open Game Content from the System Reference Document.
WEAPON FINESSE [Combat]
Prerequisite: Base attack bonus +1.
Benefit: With a light weapon, rapier, whip, or spiked chain made for a creature of your size category, you may use your Dexterity modifier instead of your Strength modifier on attack rolls. If you carry a shield, its armor check penalty applies to your attack rolls.
Special: A fighter may select Weapon Finesse as one of his fighter bonus feats.
Natural weapons are always considered light weapons.