Intercharacter interval: In asynchronous transmission, the time interval between the end of the stop signal of one character and the beginning of the start signal of the next character.

Note: The intercharacter interval may be of any duration. The signal sense of the intercharacter interval is always the same as the sense of the stop element, i.e. , "1" or "mark."

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