3D flying is when you fly in 3 dimensions
so whats a trainer flying in, 2 dimensions?!
Airplanes can't fly backwards or sideways. An airplane can only fly forward
yes they can. a high alpha knife edge harrier is more or less flying sideways, albeit slowly.
a tailslide is flying backwards is it not and if you are clever you can keep it falling backwards for a little while.
3d is flying beyond the stall using thrust vectoring and power.