like head bobbing

Ah i didnt know either oof

Tweening (or in betweening) is a process in animation where you add frames (called key frames) in animation between 2 other frames. Take a ball moving from left to right for example. One frame, the ball is on the left. The next frame, the ball is on the right. Adding a frame between the frames where the ball is in the middle adds more smoothness to the animation, but it's still choppy. You add more key frames between the left, middle and right frames. Then its smooth because you used tweening!