From TheBestCaseScenario

[edit] C.F.M.

Acronym for Cubic Feet per Minute. It shows the volume of air moved by a fan in nominal conditions. There are complicated mathematical expression to calculate this, taking into account the effective area of the fan and the linear speed of the air passing though it, but we must trust the manufacturer or an advanced reviewer for the actual number.

Regularly, the more the CFM, the better. But factors like turbulence and the 'shape' of the air stream are important too (e.g.: a blower fan moves less air than an axial one, but more uniformly, so it may give better result in a given case).

The tool used to measure air is called an Anemometer. It is used mostly in industries related to HVAC or weather measurement. Hand held versions exist and the hardcore enthusiast that works heavily with modifying airflow in a case for cooling purposes will have some version of this useful tool in their arsenal.