What is defined as a Metering Head?

Hi, Hopefully not a silly question but what parts are normally defined as the metering head on a GTI? I am looking to get a spare which I may get refurbished but, looking on a well known website, various parties seem to think it is just the black cube that the injector lines feed out of, the larger piece that sits on top of the air filter  (without the back cube) or both parts together. Secondly, I have a 89 Cabby and an 83 Campaign. Is a metering head for the 89 ( part no 026133353 B) that I have seen also compatible with the '83? Thanks for any help 

People often call the whole air box, airflow arm and fuel distributor the metering head.

For me the cast iron fuel distributor is the metering head and is what the fuel lines connect to. It is where the fuel is "metered" from, it is the position of the plunger inside the metering head that determines how much fuel flows to the injectors.

Fuel metering valve commonly referred to as fuel metering head is indeed the black cube that the injection lines connect to, looks like they are the same part number for both 83 and 89 cars but couldn't see the part number you gave

partsbase.org

thanks guys