This is the 12886th most frequent Russian word.
легковое
"Легковое" means "passenger" or "lightweight" when referring to a passenger car.
Here, 'легковая' is used as an adjective describing 'машина' (car). It specifies the type of car, indicating it's not a truck or heavy-duty vehicle but a lightweight/passenger car.
Эта легковая машина достаточно экономична.
This passenger car is quite economical.
In this sentence, 'легковое' modifies 'транспортное средство' (vehicle), emphasizing that the vehicle is lightweight and intended for personal transportation.
Легковое транспортное средство предназначено для перевозки небольшой группы людей.
A passenger vehicle is designed for carrying a small group of people.
Here, 'легковых' is the plural form of the adjective agreeing with 'автомобилей' (cars), describing the type of vehicles observed.