S: (n) channel, communication channel, line ((often plural) a means of communication or access) "it must go through official channels"; "lines of communication were set up between the two firms"
S: (n) back channel (an alternative to the regular channels of communication that is used when agreements must be made secretly (especially in diplomacy or government)) "they negotiated via a back channel"
S: (n) lens ((metaphor) a channel through which something can be seen or understood) "the writer is the lens through which history can be seen"