Spline animation
Animating a value — usually an object's or camera's position — by moving it along a spline curve over time, giving smooth, art-directed paths.
Instead of keyframing position at many points, the animator lays down a spline (Bézier, Catmull-Rom, NURBS) and drives a parameter from 0 to 1 along it; the engine evaluates the curve to get position and, often, a tangent for orientation. Catmull-Rom is popular because it passes through its control points, so artists place the path directly.
Spline animation is the backbone of camera rails in cutscenes, flythroughs, moving platforms and particle trails. A separate speed curve (easing) usually controls how fast the parameter advances, decoupling the shape of the path from the timing along it — the classic distinction between spatial and temporal control.