Changes in the animation are defined in a keyframe. When you create frame-by-frame animation, every frame is a keyframe. In tweened animation, you define keyframes at significant points in the animation and Flash creates the contents of frames between. The interpolated frames of a tweened animation appear as light blue or light green with an arrow drawn between keyframes. Because Flash documents save the shapes in each keyframe, create keyframes only at those points in the artwork where something changes.

Keyframes are indicated in the Timeline: a solid circle represents a keyframe with content on it, and an empty circle before the frame represents an empty keyframe. Subsequent frames added to the same layer have the same content as the keyframe.