It is caused when light strikes the lens and either causes the entire image to be fogged in appearance, or for a little row of polygons (the silhouette of the iris) to appear from the light hitting the surfaces of the many elements in the lens. It is solved by flagging the lens. [Go to source
Hot spot in a picture that is caused by direct light hitting the front element of the lens and reflecting through all the other glass elements in a lens.
a cool effect that occurs when internal refractions and refractions of incident light within the internals of a physical camera create bright patterns within the image