A rocket is a vehicle, missile or aircraft which obtains thrust by the reaction to the ejection of fast moving exhaust gas from within a rocket engine. Often the term rocket is also used to denote a rocket engine.
In military terminology, a rocket usually uses solid propellant and is unguided. These rockets can be fired by ground-attack aircraft at fixed targets such as buildings, or can be launched by ground forces at other ground targets. During the Vietnam era, there were also air launched unguided rockets that carried a nuclear payload intended to attack aircraft formations in flight. A missile, by contrast, can use either solid or liquid propellant, and has a guidance system. This distinction usually applies only in the case of weapons, though, and not to civilian or orbital launch vehicles.
In all rockets the exhaust is created from propellant which is carried within the rocket prior to its release. Rocket thrust is due to accelerating the exhaust gases .There are many dissimilar types of rockets, and a comprehensive list can be found in spacecraft propulsion- they range in size from tiny models that can be purchased at a hobby store, to the enormous Saturn V used for the Apollo program.
Rockets are used to accelerate, change orbits, de-orbit for landing, for the whole landing if there is no atmosphere, and sometimes to soften a parachute landing immediately before touchdown.