A circular halo or disk surrounding the head of a sacred or exalted figure in religious and symbolic imagery.
A nimbus is a halo or radiant disk surrounding the head of a sacred, divine, or exalted figure. The motif appears in several artistic traditions and became especially important in Christian imagery, where it identifies Christ, saints, angels, and other holy figures.
In sculpture the nimbus may be carved as part of the figure, attached as a separate element, pierced, gilded, painted, or represented by rays. Its shape and treatment can contribute strongly to the silhouette and iconographic identity of the figure.
Etymology
From Latin nimbus, “cloud” or “aureole,” later used for the luminous halo around a sacred figure.
Sculptor Notes
In sacred sculpture a nimbus should be treated as part of the total silhouette. Its diameter, thickness, relief, attachment, and relation to the head can either reinforce the figure's hierarchy and clarity or become a distracting appendage.
References
https://www.getty.edu/vow/AATFullDisplay?subjectid=300375684