Which term describes the transfer of information in one direction only?

The term that describes the transfer of information in one direction only is "simplex." In a simplex communication system, data can only flow in a single direction, meaning there is no return channel for feedback. This is akin to a one-way street where traffic is permitted to move in only one direction.

In terms of applications, simplex communication can be found in situations where a sender transmits information without the need for the receiver to reply. A classic example is a television broadcast, where information is sent from the broadcaster to viewers without any provision for the viewers to send information back.

The other terms refer to different types of communication channels. Half duplex allows communication to occur in both directions, but not simultaneously, much like a walkie-talkie, where one person speaks while the other listens. Full duplex allows simultaneous two-way communication, akin to a telephone conversation. Quarter duplex is a less commonly used term that typically would suggest a system that allows for more complex transmission scheduling, but it is not standard terminology in communication systems compared to the others. Thus, simplex stands out as the term specifically denoting unidirectional flow of data.