As we all know, 3D flying is the skills that takes may years to develop and hated by pilots who simply can't do it!
love that definition
My turn now: 3D flying is the mastery of using the motor's torque and thrust vs the lifting capabilities of any part of the aircraft parts vs synergy to perform figures, or a sequence of, pre- or post-stall, that usually can't be performed by full scale aircraft due to pilot/power/airframe/safety limitations...
Biggest help in learning 3D: my sim (Aerofly) and all the fantastic tuition videos, thanks to the authors!
and +1 on the comments made by ahicks and sensei