Entry 09 · the alphabet of motion
A frame drawn between two keyframes to smooth the transition.
CSS @keyframes · inbetween
The long entry
In-betweens (or tweens) are the connective tissue of animation. Once drawn by hand by junior animators, today they are computed: every CSS transition, every Lottie path, every Framer Motion animate is a request for a software in-betweener to fill the middle.