Monaural sound is an audio system in which audio signals are mixed and then routed through a single audio channel. Considered less expensive for audio reproduction and recording, as only basic devices are required, it is mainly used in hearing aids, cellphone and telephone communications, public address systems and radio communications. Mono is the preferred audio format when the focus is on clarity of a single amplified sound or voice.
Monaural sound is also known as monophonic sound or simply mono.
Techopedia explains Monaural Sound
Monaural sound is the basic format for sound output. In the case of monaural sound reproduction, only a single microphone and loudspeaker are required. It is also the same for monaural sound recording. In the case of multiple headphones or loudspeakers, the sound signals are mixed together and then fed through a common signal path. Similar to stereo sound, mono can be seen in most FM radio, NICAM stereo-oriented TV and VCR formats, compact audio cassettes and Minidiscs. However, it is not used in audio CDs and 8-track tapes.
One of the biggest benefits of using monaural sound is in the fact that the same sound level reaches all listeners. In other words, unlike stereo audio systems, monaural systems do not convey any sensation of location or depth. This factor is taken advantage of in well-designed mono systems for speech reinforcement and speech intelligibility. Compared to a stereophonic audio signal, a monaural signal has better signal strength with the same power.
Examples of monaural sound systems are mono split cluster systems and single-channel center clusters.