Folks,
What we have here is a clash of "Airplane Navigation of Dummies" and something a bit nearer to an engineering solution.
For the average pilot, the simplest definition is all that is required, a bit like the simplistic diagrams we use to illustrate the "forces" acting on an aircraft in cruise, climb and descent ( thrust, drag, lift and the CAA) --- but for an engineer it is not "that simple".
Try arguing with an engineer for an airframe or (particularly) an engine manufacturer about in-flight performance analysis versus contract guarantees --- right down to latitude and Coriolis effect --- that's really getting into the fine print.
Tootle pip!!