Colloquial term for the short signal in Morse code; the formal term is 短点 (たんてん).
See also: 短点 (たんてん)
In Morse code, 'ton' is a short sound and 'tsuu' is a long sound.
He tapped out three dots on the radio.
They sent the emergency signal using dots and dashes.
Onomatopoeic representation of the short beep sound in Morse code.