Channel

For the geographical meanings of this word, see channel (geography).

In communications, a "channel" is the "path" or "route" which a message follows, as it is transmitted between a communication source and a receiver. More specifically, in telecommunications, the term has the following definitions:

A connection between initiating and terminating nodes of a circuit.
A single path provided by a transmission medium via either
1. physical separation, such as by multipair cable or
2. electrical separation, such as by frequency- or time-division multiplexing.
A path for conveying electrical or electromagnetic signals, usually distinguished from other parallel paths.
The portion of a storage medium, such as a track or a band, that is accessible to a given reading or writing station or head.
In a communications system, the part that connects a data source to a data sink.
A specific radio frequency or band of frequencies, usually in conjunction with a predetermined letter, number, or codeword, and allocated by international agreement. For example 802.11b consists of unlicensed channels 1–13 from 2412MHz to 2484MHz in 5MHz steps.
In digital imaging, a channel is the black and white representation of a specific color; by extension, the representation of a mask — see channel (digital image)
In particular, a television channel. Examples include North American TV Channel 2 = 55.25MHz, Channel 13 = 211.25MHz
"channels" in Internet Relay Chat (IRC) which are named and based upon digital distinction as opposed to analog distinction.
An ion channel is a gate in a membrane that allows the passage of certain types of molecules.