AFM - Air Flow Meter.
Basically, there are two types of air flow controllers, the 'AFM' (Air Flow Meter), and the 'MAP' (Metered Air Pressure, I think..). The AFM uses a flow sensor on the end (or down the intake a little) of the throttle body, mechanically (but Electroniccaly controlled) allowing air to flow directly into the throttle body.
The MAP on the other hand is a vacum sensor that controls the opening of the butterfly to the Plunem chamber to allow air to flow to the cylinders this way. It is a slightly more precice way of mesuring air flow.
A Stand-alone ECU is just a box that controls particular components of the engine, by tricking the ECU into thinking it's doing all the work. A Stand-alone ECU can be hard to install, but once installed, it's essentially a set and forget thing.