tolerance field

1. The region between two curves, such as circles or rectangles, used to specify the tolerance on component size and geometry.
2. Pertaining to the cross section of an optical fiber, when used to specify the respective diameters and ovalities of, and concentricity error between, the core and cladding; two concentric annular regions which define the core-cladding boundary and the cladding outer boundary. Note: Dimensions are usually expressed in micrometers (