any of a variety of bright circles or arcs centered on the sun or moon, caused by the refraction or reflection of light by ice crystals suspended in the earth's atmosphere and exhibiting prismatic coloration ranging from red inside to blue outside
Hazy ring around bright lights seen by some patients with refractive error of optical defects
A metal ring used for patients with upper spinal cord injuries that surrounds or encircles the patient's head, allowing for proper alignment of the neck and spinal column
(n ) The region around a point in a mesh, whose values are used when updating the value of the central point In a cellular automata, the halo comprises those neighbouring cells whose values are used by the automaton's update rule