Flash can create two types of tweened animation. In the first, called motion tweening, you define properties such as position, size, and rotation for an instance, group, or type block at one point in time, and then you change those properties at another point in time. In the second, called shape tweening, you draw a shape at one point in time, and then you change that shape or draw another shape at another point in time. Flash interpolates the values or shapes for the frames in between, creating the animation.
Tweened animation is an effective way to create movement and changes over time while minimizing file size. Unlike frame-by-frame animation, Flash only needs to store the values for the changes between frames, not the entire frame.