Impedance for a communications console
This is half guess: -

By the sound of it, the unit can broadcast audio and send control data over many hundreds of metres. If so, data/control will be some form of digital signalling and without a proper terminator at the end of a long run of cable you will possible get data corruptions. This is my gut feeling.

RS485 is a data system that needs exactly the same not because of some quirk in its design but because of the laws of physics requires data terminators for long runs of data.

It looks like Zetron are still making good stuff in this area so if you have a product name or code then a link would be useful to anyone wanting to look technically deeper into this.