What is half duplex mode?

Half Duplex mode is when the same communication channel is used for transmit and Receive, and that means that communicating parties cannot Transmit and Receive at the same time.

In simple way it is one way communication e.g.  FAX, Radio, Television etc

one process at a time, either send or receive; one process at a time, in both direction of communication node.

It was no big deal. Data could only be sent or received at a time Half-Duplex mode. Its because Half-duplex mode uses one pair of wire for communication. 

 In half duplex mode. Its like one single lane used for 2 ways. At a time one way works

The half-duplex transmission is capable of sending signal in both directions, but in only one direction at a time. Some networks use half-duplex

Half-duplex data transmission means that data can be transmitted in both directions on a signal carrier, but not at the same time. One time only one direction.

WE CAN ONLY SEND INFORMATION IN ONE DIRECTION EITHER FROM SENDER TO RECEIVER OR RECEIVER TO SENDER