In animation, when you setup a pose for a character, (or vehicle, or camera, or whatever,) you set a keyframe for one point in time, usually represented on a timeline. Next you move later on the timeline, and set another pose. What about all the time 'in-between' the keyframes? The great thing about computer animation is that the computer then calculates the motion for you, and sets all the 'in-between' frames, or 'in-betweens.' Most times you can adjust how the computer interpretes the motion, and the adjustments you make are to the 'tweeners' or, the type of interpretation. Is it linear? Or, does it follow a curve? OR... does it NOT move between two points on the timeline? Then the 'tweener' would be set to 'hold' the animation for that time. Hope this helps. :> If you want, IM me for more info. Have fun!