a small rocket engine on a larger rocket or spacecraft that is fired to slow or alter its course

a rocket A rocket is a vehicle, missile or aircraft which obtains thrust by the reaction to the ejection of fast moving exhaust from within a rocket engine

A rocket so mounted on a vehicle or spacecraft that it fires in the direction opposite to the motion of the vehicle or spacecraft. Retrorockets are used to slow down the vehicles on which they are mounted.

A rocket fired to reduce the speed of a spacecraft.

A retrorocket is a rocket engine whose exhaust is directed to hinder, stop or reverse motion.

A retrorocket is a rocket engine used for providing thrust to oppose the motion of a space vehicle, thereby causing deceleration of the vehicle. When the vehicle is slowed, its orbit will decrease in altitude until the point at which aerodynamic forces begin to rapidly slow the motion of the vehicle, and it (hopefully) returns safely to the ground. Without such rockets, spacecraft would remain in orbit for years until their orbits naturally slow, and reenter the atmosphere at a much later date.