centroid, In geometry, the centre of mass of a two-dimensional figure or three-dimensional solid. Thus the centroid of a two-dimensional figure represents the point at which it could be balanced if it were cut out of, for example, sheet metal. The centroid of a circle or sphere is its centre. More generally, the centroid represents the point designated by the mean (see mean, median, and mode) of the coordinates of all the points in a set. If the boundary is irregular, finding the mean requires using calculus (the most general formula for the centroid involves an integral).