All this means is that the rotors have passages cut into them for addtional airflow. The addtl airflow helps to cool the rotors and dissapate heat. As mentioned above, only the front rotors are ventilated. This is typical for many passenger cars in our market today. The rear rotors are a solid design with no passages for cooling. As the vehicle brakes, the motion is transferred forward, so the front does most of the stopping. This is why you see larger brake components up front and also the addtional cooling, or ventilation you were mentioning.