XON/XOFF
Alternatively referred to as software flow control, XON and XOFF are control characters used in data transmission. XOFF is used by a receiving device as a way to let the transmitting device know it needs to stop transmitting. When the device is ready to recommence, the XON character is sent. With most environments, XOFF is achieved by pressing CTRL+S and XON is achieved by pressing CTRL+Q. Some Sun, Linux, and Unix computers actually have a "Stop" key on the keyboard that can be used to stop and continue text on the screen.
Also see: Flow control, On