A QIE Channel represents an interface between two (or more) systems and contains the entire configuration for managing the flow of information between the systems. A channel will always have one (and only one) data source and at least one destination. A channel will typically also contain one or more mapping and/or condition nodes which handle message routing and data manipulations.
Another way to think of a channel is as the starting point for most of the work you will do in QIE.