Thrust
Thrust is the force that pushes a rocket or spacecraft by expelling mass in the opposite direction.
Technical meaning
A rocket engine creates thrust by accelerating propellant through a nozzle. Because the vehicle carries its own propellant—and, for chemical rockets, usually its own oxidizer—a rocket can produce thrust in a vacuum. Thrust is measured as force, commonly in newtons or pounds-force.
Why it matters
Thrust determines whether a launch vehicle can lift off, how quickly it accelerates, the loads placed on the vehicle and payload, and how long a maneuver requires. Mission design considers thrust together with vehicle mass, burn duration, controllability, and specific impulse.