A lens fault that happens because glass bends different colors of light by slightly different amounts. As a result, the colors do not all focus at exactly the same point. This creates colored fringes, often purple or green, along high-contrast edges, for example dark branches against a bright sky. It can appear in many kinds of lenses, especially at wide apertures.
Lens makers reduce it with special low-dispersion glass and apochromatic designs. Much of the remaining effect can be corrected in camera or with editing software.
Do you have a better definition? Share it in the comments.
