I really find it difficult to understand the confusion.
A charter flight is chartered by a third party. This is normally a bonded tour operator. I believe I would be correct in saying that where a charter airline "sells" seats on a chartered flight, these are sold through an ATOL holder, rather than contracted directly with the airline, hence the clear differential between Monarch Scheduled and Monarch, and My Travel Airlines and MyTravelLite.
A scheduled service is sold directly by the airline itself to the punter. If a tour operator uses seats on said scheduled service, then they buy them from the carrier, and use them to sell on to their IT customers.
Then again, perhaps it is I that am confused!