Mono audio is sound that is meant to be heard as if coming from one position.
This is in stark contrast to stereophonic or stereo sound, which uses two separate audio channels. As a listener, the most striking difference is that stereo sound is capable of wide perception, whereas mono is not.
In Windows 11, if you have difficulty hearing sound from your computer, you can enable mono audio. This function allows the system to swap the stereo into a single channel to help you hear all the sounds.