Depends on the context.. But I would expect that it means internally within the organisation ... like referrals. Sales from a website would be an external sales channel because you have customers coming from outside the business. Don't quote me on that but it maybe some help.
I would of thought that it's internal communication inside of a company. Probably something like a sales rep speaking to a senior rep asking a question they don't know to provide some one with help.
Yeah, I think so however contacting customers from an internal database would generally be an outbound sales channel.