Octave
One layer of noise at a finer scale; each octave adds smaller detail on top.
See it in Noise & texture. Move Octaves from 1 to 8 and watch finer detail pile on.
In plain words
One layer of smooth noise gives soft, broad shapes. A second layer, twice as fine and half as strong, adds smaller bumps. A third adds smaller ones again. Each layer is an octave, a name borrowed from music, where each octave doubles the pitch. Clouds and mountains usually need five to eight octaves.