Weapon Finesse( Player's Handbook v.3.5, p. 102)
[Fighter Bonus Feat, General]
You are especially skilled at using weapons that can BENEFIT: as much from Dexterity as from Strength.
Base attack bonus +1,
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.
A fighter may select Weapon Finesse as one of his fighter bonus feats (see page 38). Natural weapons are always considered light weapons.