Animation is the appearance of an image changing over time. The most common types of animation in Macromedia Director MX 2004 involve moving a sprite on the Stage (tweening animation) and using a series of cast members in the same sprite (frame-by-frame animation).
Tweening is a traditional animation term that describes the process in which a lead animator draws the animation frames where major changes take place, called keyframes. Assistants draw the frames in between. Tweening in Director lets you define properties for a sprite in frames called keyframes, and Director changes the properties in the frames in between. Tweening is very efficient for adding animation to movies for websites, since no additional data needs to download when a single cast member changes.
Frame-by-frame animation involves manually creating every frame in an animation, whether that involves switching cast members for a sprite or manually changing settings for sprites on the Stage.
Other forms of animation include making a sprite change size, rotate, change colors, or fade in and out.