Network terminator

A terminator's basic function is to stop "echos" in the signal cable.

https://www.kele.com/content/blog/2014/01/17/the-rs-485-network-terminator

More or less--You clap your hands and you hear the echo from across the valley. Or you are in a long hall way and hear an echo from the open doors at the end of the hall. That is because of "impedance" mismatch.

The sound travels outwards from you in the free air--And then hits a mountain (solid wall) and reflects back. Or free travel of sound down the hall and hits the open end--Another change of "impedance" of the air column.

Same thing with electrical cable... You send a pulse down the cable and it hits an open wire (infinite resistance) and you get an echo back--Which confuses the other receivers on the signal wire.... Same thing if the signal hits a dead short, then a pulse (opposite polarity of "open wire") is reflected back... A terminator if the "characteristic impedance", matches that of the signal wire and since no impedance mismatch, the signal is not reflected.

The details do matter--One way transmission on the wire (only need terminator on receiving end of the wire). Or bi-directional line (device sometimes transmits and sometimes receive on the same wire)--Need termination at both ends.

And you can supply power (to power small devices on the cable, or hold the signal wire with a "soft" 0 or 1  level to prevent "noise" being received and confusing the systems).

And as Mike says... The same "cable plug" does not mean that electrically, the transmitters and the receivers are the same.

-Bill