In telecommunication, the term stop signal has the following meanings:

1. In start-stop transmission, a signal at the end of a character that prepares the receiving device for the reception of a subsequent character. A stop signal is usually limited to one signal element having any duration equal to or greater than a specified minimum value.

2. A signal to a receiving mechanism to wait for the next signal.

Source: from Federal Standard 1037C and from MIL-STD-188