Teletype was a trademark of the Teletype Corporation of Skokie, Illinois, USA. Founded in 1906, it became part of ATT in 1930. Operations ceased around 1990.
RO - Receive only
Teletype machines were given a model number, often followed by letters indicating the configuration:
KSR - Keyboard send and receive
ASR - Automatic send and receive (i.e. built-in paper tape reader and punch)
The one I have is a ASR-35 (an ASCII version of the model 28) made in 1967.