Inlindl School( Drow of the Underdark, p. 56)
You have learned House Inlindl's fighting techniques, which focus on using light weapons and shields.
At the start of your turn, you can choose to sacrifice your shield bonus to AC in exchange for a bonus on melee attack rolls equal to one-half that bonus. This bonus applies only on attacks made with light weapons (or other weapons to which Weapon Finesse applies). This effect lasts until the start of your next turn.