RTTY (Radio Teletype) is a method of transmitting text message by radio. Data is usually sent using the 5 bit Baudot code, although ASCII is rarely used. Much military RTTY traffic is encrypted, using methods such as KG-84.
Baudot RTTY is typically only used by ham radio operators and for transmitting public information such as weather reports and forecasts. The days of using RTTY to send news/press reports, etc are long gone.