FT8 ("Franke-Taylor design, 8-FSK modulation") is an extremely-weak-signal, digital, narrow bandwidth (50 Hz Hertz (Hz), unit of frequency, defined as one cycle per second (1 Hz). ), QSO-only communication protocol used by amateur radio ("ham radio") operators. It is popular among amateur radio operators for its ability to send signals despite challenging propagation conditions, high noise environments, low power operations (QRP In amateur radio, QRP operation refers to transmitting at reduced power while attempting to maximize one's effective range. ), or even compromised antennas.
FT8 transmits and receives only the bare essentials needed to make an amateur radio contact (QSO): Exhange of callsigns, readability report, signal strength report, and "best regards" ("73"). Because only this information can be sent, FT8 is not a "conversation" mode. FT8 transmits this minimum of information in a semi-automated fashion on its own time frame. Therefore, FT8 is not a "keyboard-to-keyboard" (real-time chat) mode.
JS8 is a variant of FT8 which allows operators to send more information and converse with each other. JS8 was created to allow the basic principles of FT8 to be applied to sending actual messages (instead of just the bare minimum QSO information that FT8 limits operators with).