Entry 17 · the alphabet of motion
A four-dimensional rotation primitive that avoids gimbal lock.
CSS @keyframes · quaternion
The long entry
Quaternions are how 3D software actually rotates things under the hood. They store orientation as four numbers (w, x, y, z) instead of three Euler angles, which means they interpolate smoothly through any rotation without flipping or stalling. You'll never type one by hand, but you'll feel the difference when a 3D animation rotates cleanly versus jankily.