Definition
A CAS number (CAS Registry Number) is a unique numeric identifier assigned by the Chemical Abstracts Service to every distinct chemical substance. The format is up to three hyphen-separated groups of digits, for example 7439-92-1 (lead), with a final check digit.
Key point
A CAS number names a substance unambiguously across languages and synonyms. That is why every material-declaration format and the Candidate List identifies substances by CAS number.
Why it matters
Chemical names vary by language, synonym and trade name. A CAS number identifies a substance unambiguously, so material-declaration formats like IEC 62474 and IPC-1752A reference substances, including SVHCs, by CAS number rather than by name.