Referring to the coat pattern where the hair lacks the normal agouti banding pattern, and instead has very wide bands that that make the majority of the coat white except at the very tips which show the base colouration (black, blue, chocolate etc.). Called Shell when red/cream colouration is involved; Genetically they are silver tabbies and their base colour (black/chocolate/cinnamon and their dilute forms) with modified agouti banding. See Chinchilla.

SOURCE: cat-world.com.au