In data networking, what is defined as "Signals may flow in either direction, but not simultaneously"?

The definition "Signals may flow in either direction, but not simultaneously" accurately describes half-duplex communication. In half-duplex systems, devices can send and receive data, but they cannot do so at the same time. When one device is transmitting, the other must wait until the channel is free to send its own data. This is particularly relevant in scenarios where the medium for communication has constraints that prevent simultaneous transmissions, ensuring that signals do not collide.

In contrast, full-duplex systems allow data to be sent and received simultaneously, enabling more efficient communication. Simplex refers to communication that travels in only one direction, with no return path for signals. The term bidirectional could imply the capability of both sending and receiving but does not specify the nature of the transmission being simultaneous or not. Therefore, half-duplex is the correct answer for the given definition.