Tweening is a computer-assisted animation technique. It consists in moving or morphing a digital element between 2 keyframes. This by using an animation software.
Traditional animation is an animation technique that consists to give the illusion of movement by projetting a series of drawings in front of our eyes.
The 12 basic Animation Principles where created and described in the reference book for animators : "The illusion of life". This book was co-written by 2 top 2D Disney animators