Drag coefficient is a numerical value that represents a vehicle's resistance to air. It works as it moves forward. These measures depend on fuel efficiency, speed, and performance. If a car has a lower drag coefficient that means the car can cut through air more easily. It works like when a car movs it encounters air resistance. By some vehicles this measure can be like Sports Cars 0.25, Electric Vehicles ~0.20 -- 0.25 or Trucks has ~ 0.35 -- 0.45. Also this drag coefficient depends on cars smooth designs reduce drag, larger frontal areas and higher speeds of a car. 

Key Points 

Body Shape is an important factor to make sure a car has smooth surfaces that reduce drag. 

Underbody Design is a flat. Which covered underbody minimises turbulence. 

Spoilers and Aerodynamic Aids basically help direct airflow efficiently.

Wheel Design always covered or streamlined wheels can lower drag. To know more about Wheel Design check out CarSell Wheel Design full definition with details. 

Importance 

Drag coefficient is a key factor in a car. If it is a perfect example of automotive design, balancing efficiency, performance, and aesthetics then buyers must have to know about Drag coefficient. To enjoy fuel savings and smoother rides try to choose a car with lower Cd values.