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An Altocumulus is a cloud belonging to a class characterized by globular masses or rolls in layers or patches, the individual elements being larger and darker than those of cirrocumulus and smaller than those of stratocumulus. These clouds are of medium altitude, about 8000-20,000 ft (2400-6100 m). A middle cloud, usually white or gray, often occurs in layers or patches with wavy, rounded masses or rolls. Altocumulus often are seen preceding a cold front, and their presence on a warm, humid, summer morning frequently signals the development of thunderstorms later in the day.

One form of altocumulus, altocumulus lenticularis, or mountain wave, is frequently reported as "UFOs".