You can consider an anology of toggling a button on or off of an appliance.
Here, it is called Software Flow Control (X/on X/off flow control). The "X" stands for "transmitter" and X/on and X/off represents the signals to turn the transmitter on or off. The X/on signal has same bit configuration as ASCII Ctrl-S keys combination. This pauses the transmission of the data as if the electric flow is stop when off button is pressed. Similarly, X/on has same bit configuration as ASCII Ctrl-Q keys combination. It resumes the flow of the data transfer as if electric is started again when on button is pressed.
Here, it is called Software Flow Control (X/on X/off flow control). The "X" stands for "transmitter" and X/on and X/off represents the signals to turn the transmitter on or off. The X/on signal has same bit configuration as ASCII Ctrl-S keys combination. This pauses the transmission of the data as if the electric flow is stop when off button is pressed. Similarly, X/on has same bit configuration as ASCII Ctrl-Q keys combination. It resumes the flow of the data transfer as if electric is started again when on button is pressed.