A mosaic is basically any mutation crossed with a white. Most commonly when a white is bred to a standard. Mosaic patterns are random. There are special terms for common patterns.
– A chinchilla seen with white fur, grey ears, black eyes, and a grey tail with no markings or minimal markings is called a "Wilson White" in the USA. A "Wilson White" is any white chin in the UK.
– A Chinchilla that is heavily marked or marbled is called an "extreme mosaic" because the harsh contrast.