What does 'simplex' refer to in data transmission?

The term 'simplex' in the context of data transmission refers specifically to a communication method that transmits signals in one direction only. This means that data can only be sent from the sender to the receiver, without the capability for the receiver to send data back to the sender simultaneously. An example of simplex transmission is a traditional television broadcast, where the TV signal is sent to the receiver without any return communication from the viewer.

This is distinct from other types of transmission methods. For instance, 'duplex' refers to systems that allow signals to be transmitted in both directions, either simultaneously (full duplex) or alternately (half duplex). The mention of high frequency signals or the ability to transmit in either direction relates to other communication characteristics that do not define simplex transmission directly. Simplex is strictly bound to the one-way nature of the signal flow.