The creation, manual or algorithmic, of frames of animation 'twixt keyframes.
Shorthand for inbetweening, tweening originally was developed as a means of simplifying the storyboarding and artistic process in animation. The lead artist would design only the keyframes of animation to observe the progression - once the animation was approved, tweeners would draw out all of the frames between each keyframe.
Advances in computer graphics have since allowed tweening to be automatically generated, and it has become an essential tool in all forms of animation.
Use this tag when dealing with tweening issues in the animation of your game's entities. It can apply equally to manual tweening and software-generated tweening.