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1. (Science: ophthalmology) Any error that results in image degradation. Such errors may be chromatic, spherical, astigmatic chromatic, distortion, or curvature of field: and can result from design or execution, or both.

2. (Science: physics) failure of an optical or electron-optical lens to produce exact geometrical (and chromatic) correspondence between an object and its image. In a video camera tube or cathode-ray tube, aberrations are when the (electrostatic or electromagnetic) lens does not bring the electron beam to sharply focused points uniformly on the target or screen, or to correct geometrical positions, as the beam is deflected.

3. (Science: zoology) a term which, if used to denote a number of individuals within a species, unequivocally signifies infrasubspecific rank.

See: aberration, chromatic, aberration, spherical.