The acronym for actual cubic feet per minute, which is the actual gas flow rate expressed in the American Engineering system of units. ACFM is a measure of the volume of gas that passes a given point during a one-minute period.
When manufacturers list performance for blowers and compressors it is stated as "Capacity" in CFM (Cubic Feet per Minute). This refers to the volume of air at the inlet to the unit, therefore this is often referred to as Inlet CFM (ICFM) or Actual CFM (ACFM). These terms are used interchangeably and mean basically the same thing (CFM, ICFM, ACFM).