Physically speaking, a Channel is the passage way a signal or data is transported. In case of audio files, it’s the passage or communication channel in which a sound signal is transported from the player source to the speaker.
An audio file can contain one, two or even more Channels. Especially in the case of surround sound, more audio Channels are needed to create the feeling of sound being – as the name suggests – all around the listener.
The value found with the Channels information of a files metadata indicates the actual amount or number of Channels in the audio file. One Channel is usually referred to as mono, while more Channels could either indicate stereo, surround sound and the like.