It's being called a data diode (diodes usually allows current in one direction only).
It can be implemented with a fiber optics cable with only the transmitter on the secure side, a laser+photo cell for real air gap, cutting the rx cable in a rs232 or having a microcontroller with an output pin connected to another controllers input pin. By handling it with hardware instead of software you get a very secure partition between the trusted and untrusted side.
It's used to monitor for example industrial systems and power plants.
It can be implemented with a fiber optics cable with only the transmitter on the secure side, a laser+photo cell for real air gap, cutting the rx cable in a rs232 or having a microcontroller with an output pin connected to another controllers input pin. By handling it with hardware instead of software you get a very secure partition between the trusted and untrusted side.
It's used to monitor for example industrial systems and power plants.
Wikipedia calls it unidirectional network: https://en.wikipedia.org/wiki/Unidirectional_network