MAF = Mass Air Flow sensor (aka "hot wire maf). It measures air flow by how much a heated wire is cooled.
MAP = Manifold Absolute Pressure sensor (measures the pressure / vac of the manifold).
AFM = Air Flow Meter (like LineC said, it uses a flap door connected to a potentiometer to measure air flow).
Some SAFC's will work on AFM's, but since most cars these days use a MAF, most SAFC's are programmed to work w/ a MAF.