The term thruster has a modern definition which is not given by our beloved but aged Webby. It has come to mean a device or system which provides direct thrust specifically for maneuvering a vehicle.
In nautical use, ships can have bow thrusters and stern thrusters which are differentiated from their main engines specifically by their ability to provide motive force along axes other than the vessel's long axis - along which the main engines are used, either operating normally or in reverse.
On spacecraft, thrusters refer to small rocket motors which operate either by burning propellant or by venting compressed gas in order to provide highly-controlled thrust, again usually along axes other than the vehicle's normal direction of travel.
Some sources (Merriam-Webster, for example) use the term to describe any system which provides motive power by direct expulsion of a jet. Technically, then, any form of vehicle power which operates in this manner can be termed a 'thruster'. However, generally, it indicates that the system in question is used to affect the vehicle's orientation (rotation), or to provide small translational change, rather than to provide motive force along the vehicle's primary axis of travel.
Also associated with poodles.