Sources: Player's Handbook
Epic Level Handbook
You can fire multiple arrows simultaneously against a nearby target.
Prerequisite: Dex 17, Point Blank Shot, Rapid Shot, base attack bonus +6
Benefit: As a standard action, you may fire two arrows at a single opponent within 30 feet. Both arrows use the same attack roll with a -4 penalty) to determine success and deal damage normally (but see Special).
For every five points of base attack bonus you have above +6, you may add one arrow to this attack, to a maximum of four arrows at a base attack bonus of +16 or higher. However, each arrow after the second adds a cumulative -2 penalty on the attack roll (-6 for three arrows and -8 for four).
Special: Regardless of the number of arrows you fire, you apply precision-based damage (such as sneak attack damage) only once. If you score a critical hit, only the one of the arrows deals critical damage; all others deal regular damage.
A 6th-level ranger who has chosen the archery combat style is treated as having Manyshot even if he does not have the prerequisites for it, but only when he is wearing light or no armor.