Mammatus, also known as mammatocumulus (meaning "mammary cloud" or "breast cloud") is a meteorological term applied to a cellular pattern of pouches hanging underneath the base of a cloud. The name mammatus, derived from the Latin mamma (meaning "udder" or "breast"), refers to a resemblance between the characteristic shape of these clouds and the breast of a woman. Mammatus are most often associated with the anvil cloud and also severe thunderstorms. Mammatus may appear as smooth, ragged or lumpy lobes and may be opaque or semitransparent. Because mammatus occur as a grouping of lobes, the way they clump together can vary from an isolated cluster to a field of mamma that spread over hundreds of miles to being organized along a line, and may be composed of unequal or similarly-sized lobes.