From D&D Wiki
You are equally adept at using either hand.
Prerequisite: DEX 15+
Benefit: You ignore all penalties for using an off hand. You are neither left-handed or right-handed.
Normal: without this feat, a character who uses his or her off hand suffers a -4 penalty to attack rolls, ability checks, and skill checks. For example, a right-handed character wielding a weapon with her left hand suffers a -4 penalty to attack rolls with that weapon.
Special: This feat helps offset the penalty for fighting with two weapons. A ranger wearing light armor or no armor can fight with two weapons as if he had feats ambidexterity and two-weapon fighting.