"Thrust reversal, also called reverse thrust, is the temporary diversion of an aircraft engine's exhaust or changing of propeller pitch so that the thrust produced is directed forward, rather than aft. This acts against the forward travel of the aircraft, providing deceleration. Thrust reversers are used by many jet aircraft to help slow down just after touch-down, reducing wear on the brakes and enabling shorter landing distances. It is also available on many propeller-driven aircraft through reversing the controllable pitch propellers to a negative angle."
http://en.wikipedia.org/wiki/Thrust_reversal
oppure
http://it.wikipedia.org/wiki/Inversori_di_spinta
