What term describes an amateur station that is transmitting and receiving on the same frequency?

When two amateur radio operators communicate directly with each other by transmitting and receiving on the exact same frequency, it is called "simplex" operation. This is the simplest form of communication, commonly used on VHF/UHF when stations are close enough to hear each other directly without the aid of a repeater. In contrast, "duplex" (or half-duplex) involves transmitting on one frequency while receiving on another, which is the standard method for communicating through a repeater. "Multiplex" and "diplex" refer to combining multiple signals or using single antennas for multiple bands, which does not describe basic single-frequency transmit and receive operation.