- A reddish yellow ring surrounding the optic disc, due to a widening of the scleral ring making the deeper structures visible.
- An anular flare of light surrounding a luminous body or a depigmented ring around a mole.
- A circular metal band used in a halo cast or halo brace, attached to the skull with pins.
See: halo nevus
[G. halōs, threshing floor on which oxen trod a circle; the halo round the sun or moon]