n. A ring-like space or area contained between the circumferences of two concentric circles.n. In anatomy, a ring-like part, opening, etc.: used in Latin phrases.n. (See below.) In botany: The elastic ring which surrounds the spore-case of most ferns.n. In mosses, an elastic ring of cells lying between the lid and the base of the peristome or orifice of the capsule.n. In fungi, the slender membrane surrounding the stem in some agarics after the cap has expanded.n. In zoology: A thin chitinous ring which encircles the mantle in the Tetrabranchiata, connecting chitinous patches of the mantle into which the shell-muscles are inserted.n. In entomology, a narrow encircling band, generally of color; sometimes a raised ring.n. In astronomy, the ring of light seen about the edge of the moon in an annular eclipse of the sun. See annular eclipse, under annular.n. In the Equisetaceæ, the sheath below the spike formed by the union of the bases of the leaves.n. In diatoms, the rim of silex formed within the frustules of some genera.n. The fleshy rim of the corolla in milkweeds.n. One of the external subdivisions of the body of a leech, resembling a segment of the body of an earthworm.