The drag coefficient is a dimensionless number that quantifies the drag or resistance of an object in a fluid, such as air or water. It helps to predict how easily an object can move through a fluid, with lower values indicating less resistance. The drag coefficient depends on factors like the shape of the object, its surface roughness, and the flow conditions of the fluid. In engineering and aerodynamics, the drag coefficient is crucial for designing vehicles, such as cars and airplanes, to improve fuel efficiency and performance. For example, a streamlined shape can significantly reduce the drag coefficient, allowing cars and airplanes to travel faster and consume less energy.