Sentence:  A <WSD>tween</WSD> is a method of creating animation, where you tell Flash where to start and where to end, and Flash does all the work in the middle. There are three types of <WSD>tweens</WSD>: Classic, Shape, and Motion. 
Meaning of the word marked with <WSD> tags:  An action of '''tweening''' (inserting frames for continuity); a sequence of frames generated by tweening.