CAS Number Registration
In the field of chemistry and medicine, CAS refers to the Chemical Abstracts Service (CAS) under the American Chemical Society (www.acs. org). CAS number registration is just one of the tasks of the Chemical Abstracts Agency, which is to give each substance in the literature a number to avoid the trouble of chemical substances having multiple names and make the database retrieval more convenient.
For details, please read: https://www.acs.org/content/acs/en/education/whatischemistry/landmarks/cas.html