It refers to the amount of wind or air exhaust fan included in the total volume per minute, if calculated according to cubic feet, the unit is the amount of wind CFM; if you press m to count, that is CMM. Air flow cooling fan units often use the CFM (about 0.028 m3 / min).
Wind is the most important indicator to measure the cooling capacity of the cooling fan. Obviously, the greater the amount of air cooling fan its cooling capacity is also higher. This is because the heat capacity of the air ratio is constant, the greater the amount of wind, that is, more air per unit of time can take away more heat. Of course, the same amount of wind cooling effect of wind flow situation the way.

Wind pressure
Air pressure and air flow are two opposing concepts. In general, firms in the cost considerations, to design air volume fan, it is necessary to sacrifice some of the pressure. If the fan can bring a large amount of air flow, but the pressure is small, the wind not blowing the radiator at the bottom (which is why a high number of fan speed, air volume is large, but the cooling effect is not good reason), conversely, it often means big pressure on the small amount of wind, there is not enough cold air and the heat sink for heat exchange, the cooling effect will be bad.