Propulsion refers to the process by which an object is moved or propelled through a medium, such as air, water, or space. This can be achieved in several ways including using mechanical means like engines and motors, or through natural forces like wind or gravity. The term "propulsion" often specifically refers to methods of moving vehicles or objects through the air, such as by jet propulsion (using high-speed jets of air) or rocket propulsion (by expelling hot gases).