The type of force that opposes the motion of an object through a fluid is called drag force. Drag acts opposite to the direction of the object's velocity as it moves through air or water, slowing it down. The magnitude of drag depends on several factors, including the object's shape, speed, and the fluid's viscosity. Understanding drag is crucial in fields like aerodynamics and hydrodynamics, where it impacts the design of vehicles, aircraft, and marine vessels to enhance performance and fuel efficiency.