Meaning – The term idle character, refers to a character transmitted on a telecommunication line that is not intended to represent data and does not result in an output operation at the accepting terminal.
In data communications, a character transmitted to keep the line synchronized when there is no data being sent. It also refers to a term used to describe when something is operating but is not being used.
The start and stop bits are used in asynchronous communication as a means of timing or synchronizing the data characters being transmitted.
Without the use of these bits, the sending and receiving systems will not know where one character ends and another begins.
Another bit used to separate data characters during transmission is the mark (or idle) RS bit. This bit, a binary 1, is transmitted when the communication line is idle and no characters are being sent or received.
Example of usage – “An idle character is an alphanumeric or digital character that is transmitted over a communications line but does not appear in the output of the receiving terminal.”