CAS (Chemical Abstracts Service) is a registry of chemical identification numbers maintained by the American Chemical Society. Although ceramic materials are generally minerals or processed minerals rather than chemicals, most do have numbers in the system. However many of the numbers do not have a high level of specificity (e.g. there is one number for kaolins, one for feldspars, one for clays). CAS numbers make it easier and faster to search online databases since the name of a given material can have many forms (sometimes dozens). Since regulatory bodies in many countries require that companies and individuals keep good records of the nature and hazards of the materials they have on hand, reference to these numbers is valuable.
CAS number system on Wikipedia
Understanding Acronyms on MSDS's
Understanding the meaning and purpose of acronyms used on materials safety data sheets for ceramic minerals and materials