3D is high alpha flight.. i.e. the plane is "flying" only on thrust from the prop moving over the surfaces. The wing (or fuselage) is not generating lift by forward flight... hovers, waterfalls, harriers, KE Harriers, blenders, flat spins, elevators, harrier circles, etc....

Here's a good measure ... its 3D when you cut the throttle and the plane drops like a brick!

DP