An infralateral arc (or lower lateral tangent arc) is a rare halo, an optical phenomenon appearing similar to a rainbow under a white parhelic circle.
The shape of an infralateral arc varies with the elevation of the Sun.
Between sunrise and before the observed Sun reaches about 50° over Earth's horizon, two infralateral arcs are located on either side (e.g. lateral) of the 46° halo, their convex apexes lying tangental to the 46° halo.
[1] Infralateral arcs form when sunlight enters horizontally oriented, rod-shaped hexagonal ice crystals through a hexagonal base and exits through one of the prism sides.
[1] They are often observed together with circumscribed halos and upper tangent arcs.