- either of two systems of clicks and pauses, short and long sounds, or flashes of light, used to represent the letters of the alphabet, numerals, etc.: now used primarily in radiotelegraphy by ham operators.
- a telegraph code formerly used internationally for transmitting messages; it was superseded by satellite technology (the Global Marine Distress and Safety System) in 1999. Letters, numbers, etc, are represented by groups of shorter dots and longer dashes, or by groups of the corresponding sounds, dits and dahs, the groups being separated by spaces
