MAF = Mass Air Flow sensor.

MAS (no idea why it's called that) is a cigarette packet sized box that plugs into the system via a multi-way connector. It is locked in place by a knob on top.

This MAS box does replace the fuel pump relay of earlier systems and is found in later KE-Jetronic systems.

It may also feature in the HFM systems of the original poster's vehicle but I don't know.

RayH