A uniform, featureless layer of cloud resembling fog but not resting on the ground; when this very low layer is broken up into irregular shreds, it is designated as fractostratus; 300-600 m; widespread irregular stirring and lifting of the shallow layer of cool, damp air near the ground.
Source:
PAC, 1990, 62, 2167. 'Glossary of atmospheric chemistry terms (Recommendations 1990)' on page 2180 (https://doi.org/10.1351/pac199062112167)