What is the definition of a compact car ?

A compact car can be defined as a small and economical vehicle. This car has very less volume inside the car.

Compact car is a vehicle size class — predominantly used in North America — that sits between subcompact cars and mid-size cars. The present-day definition is equivalent to the European C-segment or the British term “small family car”. However, prior to the downsizing of the United States car industry in the 1970s and 1980s, larger vehicles with wheelbases up to 110 in (2.79 m) were considered “compact cars” in the United States.

The U.S. Code of Federal Regulations and It Still Runs define compact car as a North American vehicle class that lands between mid-size and subcompact vehicles. … Small, or compact, cars have between 100-109 cubic feet of combined passenger and cargo volume, and are between 161 and 187 inches long.