Onion-ring Bokeh
Concentric rings visible inside out-of-focus highlights, caused by tooling marks on a moulded aspherical element.
In depth
Precision-ground aspherics are smooth, but the cheaper moulded and hybrid variants used in many modern lenses can retain microscopic circular ridges from the manufacturing process. These are invisible in the sharp parts of the image but are magnified into visible rings within defocused specular highlights. Nothing in processing removes them.
Examples in practice
Christmas lights behind a subject render as discs filled with faint tree-ring patterns rather than smooth circles.