The creature can change direction quickly while flying.
Prerequisite: Fly speed.
Benefit: A flying creature with this feat can change direction quickly once each round as a free action. This feat allows it to turn up to 180 degrees regardless of its maneuverability, in addition to any other turns it is normally allowed. A creature cannot gain altitude during a round when it executes a wingover, but it can dive. The change of direction consumes 10 feet of flying movement.
Source: Monster Manual (version 3.5), page 304.