CAS number
In short A unique registry number assigned to a chemical substance by the Chemical Abstracts Service.
The number identifies a compound regardless of trade name or spelling. Two product pages showing the same CAS number describe the same molecule. The final digit is a check digit calculated from the others, so a made-up number fails a simple lookup.
Research blends of several peptides have no CAS number of their own, because a CAS number designates exactly one substance. On those pages the composition is given instead.