noun

• (geometry) The standard representation of such a space in 3-dimensional Euclidean space: a surface or solid formed by rotating a closed curve, especially a circle, about a line which lies in the same plane but does not intersect it (e.g. like a ring doughnut).
• (topology) A topological space which is a product of two circles.
• {{lb|en|topology|in combination|n'''-torus|4-torus|etc.}} The product of the specified number of circles.
• A ring-shaped object, especially a large ring-shaped chamber used in physical research.
• (architecture) A large convex molding, typically semicircular in cross section, which commonly projects at the base of a column and above the plinth.
• (anatomy) A rounded ridge of bone or muscle, especially one on the occipital bone.
• (botany) The end of the peduncle or flower stalk to which the floral parts (or in the Asteraceae, the florets of a flower head) are attached.
• (botany) The thickening of a membrane closing a wood-cell pit (as of gymnosperm tracheids) having the secondary cell wall arched over the pit cavity.