ALTOCUMULUS

White or grey, or both white and grey, patch, sheet or layer of cloud, generally with shading, composed of laminae, rounded masses, rolls, etc., which are sometimes partly fibrous or diffuse and which may or may not be merged; most of the regularly arranged small elements have an apparent width of between one and five degrees.

WMO (1957) International Cloud Atlas, as cited in H. R. Byers (1974) General Meteorology