The condition of a surface of revolution where all points of the surface are equidistant from the center of the surface. If the part shown below was perfectly round then the dial caliper would measure the same dimension at any point around the diameter. See also out of round
A characteristic that all parts of a circle are identical. The measurement of roundness is essentially a measurement of the change in radii, and the roundness error is the measurement between the minimum and maximum radii in one lateral plane.