Morse code is widly used in last century, it is a method of transmitting text information. it is a series of "dit" (·), "dah" (–) and so on, when you receive it, could tranlste them to text again.
Longer mark, dash or "dah" (–) — three time units long
To short mark, dot or "dit" (·) — "dot duration" is one time unit long
To medium gap (between words) — seven time units long
To short gap (between letters) — three time units long
inter-element gap between the dots and dashes within a character — one dot duration or one unit long